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FOSSILS are the remains or indications of an

organism that lived in the geologic past.

Most living things break down when they die with the help of decomposing organisms, and from chemical &/or physical weathering. In order for something to become fossilized it must be located in a spot where the decomposing organisms and weathering can't complete their work. That usually means that the remains must be covered relatively quickly with sediments. The sea was a good environment for getting covered and preserved.

Other ways of being preserved: • Death in a dry cave could mummify an animal. • In cold climates an animal could be frozen in ice. • An animal could be immersed in tar, lava or quicksand, or

buried in a bog.

The most common fossils.are formed when minerals in solution enter the hard remains of the animal or plant and fill the spaces­and turn the remains to stone (petrifaction). The actual parts may remain or they may be replaced with minerals.

Sometime, ifa soft-bodied animal or plant is covered with sediment, all that will remain is a thin layer of carbon (carbonization), which looks like a black silhouette.

A mold remains if the imprint of the form remains after the original is gone (dissolved or broken away). Shell molds are common, both of the outside (external mold) and inside (internal mold) of the shells.

A cast is formed if the mold filled up with material that reproduces the form of the original.

Trace fossils are the tracks, burrows, and borings of animals and may be the only clue to an animal's presence, or may help the scientist (Paleontologist) understand how and in what environment an animal lived.

Major Groups of Fossils found in the Cretaceous Formations n

URCHINS, STARFISHES, etc. Echinoid~- (Means: "spiny") Sea biscuits ~ U rehins · . ,~~:.~.;. .... •

, :., ; ~ ..

SNAILS Gastropods-(Mea!'s: "stomach foot") Sea snails (mostly internal molds)

~ Q ~. AMMONITES, SQUID, etc. ;;E.

Cephalopods-(Means: "head foot") Ammonites Chambered nautilus Squid Octupus

ALGAE (Aquatic plants)

Porocystis

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F 0 S S I L S - are the remains or indications of an organism that liued in the geologic past.

Most liuing things break down when they die with the help of decomposing organisms. In order for something to become a fossil it must be located in a spot where the decomposing organisms can't do their worle. That usually means that it lDust be cooered quickly with sediments. (other ways of being preserued: -a dry caue could mummify an anima.,. It could be frozen in ice, immersed in 1ft[, lAllA. or quicksand, or buried in a .IUUJ). The sea was a good enuironment for getting couered and preserued.

The most common fossils are formed when minerals in solution enter the hard remains of the animal or plant and fill the SDaces- and turn the remains to stone. (petrification). The actual parts may remain or they may be replaced with minerals.

Sometime, if a soft bodied animal or plant is couered with sediment, all thot will remain is 8 thin layer of carbon (earbanizatiaaJ, which looks like 8 black silhouette.

R mold remains if the imprint of the form remains after the original is gone (dissolued or broleen away). Shell molds are common, both of the outside and inside of the shells.

A cllst remains if the mold fills UP with material that reproduces the form of the original.

Trace fossils are the tracks, burrows, and borings of animals and may be the onlg clue to an animals presence, or may help the scientist (PaleD.talagist) understand more about how an animalliued.

The area around Austin mas II sea in the Cretaceous period for many millions of years (70 to 100 million yeurs ago), and during that time thousands of feet of depOSits of lime, mud and animal remains collected and turned into the limestone we see Bround the hill country and in the creeks around here. Shoal Creek cuts through 8 formation that has many fossils.

Rules in creelc- set limits, stay out of water, listen for tall to return to teathers and do 8 show and tell. (Limit ahead of time how many fossils eath thild may take with them. Three is 8 good number. Tell them they may come batk with their families and collett as many 8S they like .•

LLANO COUNTY---+---BURNET COUNTY-·lt-----TRAVIS COUNTY RILEY Balcolle.

MOUNTAINS SpIcewood Fault

I I . IDOD •

D

.... W -IDDD W ~

~ -4DDD Z 2 .. ·~DDD <I > W ~ -'DDD w

.tD,DDD

-.~,DOD

Btl KL

Crelaceous KU-Upper KL-Lower

k~~:~~ Packsaddle

Schist

CRATONIC ROCKS

U 8 Carboniferous Ordovician

8 ~ + 1m + +

Volley Spring Town MIn. Gneiss Gronite

~ Cambrian

m P I

Precambrian undivided

.,

D

.... -IDDD W

W ~

-4DDD ~ Z 2

-~DDD 4 > w

-.ODD ..J w

-to.DDO

OUACHITA STRUCTURAL BELT ROCKS

D ~ • 8 Block slatl, UpPlr Paleazpic Lower Paleozoic

oql? rocks rocks

Flo. 2. Schematic aeetion, centnl Llano County to eatem Ttavia County, Tena.

Cretaceoul Lower CretaceoUi

Fredericksb1ll'l Division Edwards Limestone Comanche Peak Llmeltone Walnut Formation

Keys VaUey Marl Cedar Park Limestone Bee Cave Marl Bull Creek Limestone (included with Olea

Rose Limeatone on AustiD ud LIuo Sheets of tbe Tesu Oeologic Atla)

Trinity Division Upper Trinity

Glen Rose Limestone Hensel Sand

Middle Trinity Cow Creek Limestone Hammett Shale

Lower Trinity Sycamore Sand

Pennsylveian Lower PennsylYUlian

StraW1l Group Smitbwfek Sbale Marble FaUs Limestone Unnamed phOlpborite

Misaiaippian Barnett Formation Chappel Limestone

Miaisal ppian. and Dewnim Houy Formation

Doublehom Shale Iva Breccia

SUuriaD

Bear Sprinl Formation Unnamed Hmestone Sbibliq Formation pmar Bluff Limestone

Starcke Limeltone

OrdoYicIaD Upper Ordovici.lft

Bm'IWD Limestone Lower OrdoYlcian

EUenburpr Oroup Hone,m Formation Oormus Formation Tuyud Formation (put)

Staendebaeb Member • 'lbreadgill Member (part)

Cambrian and Ordovician • Tanyard Formation (part).

Threadgill Member (part) WlJbenq Fonnatlon (put)

San Saba Member (part) Cambrian

UPPU.Cambrian Wilhema Formation (part)

San Saba Member (put) Point Peak Member MorpD Creek Ljmestone Member Welge Sandstone Member

Riley Formation (part) Lion Mountain Sandstone Member Cap Mountain Limestone Member (part) Hickory Sandstone Member (part)

Middle Cambrian (1)

Precambrian

Cap Mountain Limeltone Member (part) lUekory Sandltone Member (part)

IgneoUi roeks Llanite (quartz porphyry dikes) Six mile Granite Oatman Creek Granite Town MOUDtain Granite

Meta-l,neaUi row Metagabbro and metadlorite

Red Mountain Gneiu Bil Branch Gneiss

Metuedimentary rocks (Ie. Clabaugh and McGehee, p. 14, for subdivisions)

Packsaddle Schist Lost Creek Gneiss Valley Sprint pneia

FOSSILS SCRIPT

Today we are going to study about fossils.

What is a fossil? Fossils are the remains of plants and animals that have become rock.

The fossils we find in Austin are fossilized remains of animals that live in the ocean. Why would we find fossils of ocean animals here in Austin? Austin was once covered by a shallow sea. (Show map of present coastline of Texas, then map of Cretaceous Austin - 100-65 million year~ ago.)

We find fossils of sea animals here because this area was once covered by a shallow sea, but the story of our fossi Is begins before that.

Do you know what tectonic plates are? They are like gigantic puzzle pieces under all of the land area of the earth. They are constantly moving.

About 300 million years ago, the tectonic plate that the South American continent rests upon moved very quickly and hit the tectonic plate that the North American continent rests upon. When this happened a large mountain range was formed. These were the Ouachita Mountains and they crossed from what is now Arkansas through the Dallas-Ft. Worth area, down through the Waco area, past the Austin area and out to what is now far West Texas. The mountains sank about 200

U million years ago. You can ~iII see the Ouachita Mountains in Arkansas, but they sank completely in Texas. They become very important in our story later on.

About 150 million years ago, the ocean moved up and covered this area. For about 50 million years the ocean would cover this area and then retreat. Throughout those 50 million years, millions of sea animals were living and dying in that sea. When they died, they floated down to the floor of the ocean and became embedded there.

About 100 million years ago, the ocean covered this area and remained for about 25 million years. More and more sea animals died and floated to the ocean floor and became embedded there. About 75 million years ago the Rocky Mountains started to erode. Sediments from this erosion came down to central Texas through streams and rivers. These deposits pushed the sea back to where it is today.

The sediments deposited were much heavier than the deposits that had been the ocean floor. After about 15 million years of the heavier sediments causing stress on the softer sediments beneath them, the softer sediments could no longer support the heavier sediments, and there was a crack or "fault" where the Ouachita Mountains once sank. In this area we call that crack the Balcones Fault. When this fault occurred, it opened up layers and layers of sea creatures that had died and become rock. Every time it rains, more fossils are washed out of the fault and are deposited in the creek beds in the Austin area.

Demonstrate fossil formation using clay and seashell:

Pretend this shell is a sea creature. It is swimming along and it dies. It floats to the bottom of the sea. In order for it to become a fossil, it must quickly be covered by sediments. If it is not quickly covered by sediments, it will simply decompose (decay). If it is quickly covered by sediments, it still decomposes, but as the body decomposes, minerals and sediments move in to take the place of where the body has been. When exposed to air and heat, those sediments and mineral harden and become rock.

There are three main types of fossi Is:

Cast fossilsare the most common types we find in this creek. (Show large clam.) A cast fossil is in the shape of the plant or animal itself.

Mold fossilsare the imprints of a pla~t of animal. (Show mold fossil.)

Trace fossils are the track of an animal. (Show ·worm track" fossil.)

Now let's look at the kinds of animal fossils we will find in Shoal Creek.

Procedure:

Show examples:

EXOGYRA (oyster) - show examples with and without "back doorn. It is also called "ram's horn" (Show picture.)

GRYPHAEA (oyster) - also called "devil's toenail"

PELECYPOD (clam)

GASTROPOD (snai I)

ECHINOID (sea urchin)

CEPHALOPOD (ammonite)

Also show limestone, calcite, pyrite nodule, conglomerate sedimentary rock with fossils, chert.

Give creek rules: 1. No throwing rocks. 2. No getting in water. 3. No running. (Limestone is slick!) 4. Boundaries

Supervise students and identify their finds. They may keep three objects from creek.

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Presentation Outline

Minerals, Rocks and Fossils (3rd-6th)

I. One Group (Three 40 min. stations-l instructor)

A. Resources 1. School Programs MRF boxes

B. Instruction 1. Mineral station and activity (see training manual) 2. Rock station and activity (see training manual) 3. Fossil station and fossil hunt (see training manual)

ll. Two Groups (Three 40 min. stations-2 instructors)

*Resources and instruction are the same except two instructors rotating stations

m. Three Groups (Three 40 min. stations-3 instructors)

*Resources and instruction are the same except three instructors rotating stations

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Presentation Outline

Fossil Hunters (K-2)

I. One Group (Two Stations--Fossil intro and showing fossilsl fossil hunting in Shoal Creek-! instructor)

A. Resource requirements 1. School Programs Fossil box

a. 9ne complete set of fossils b. Charts and map c. Clay and shell for fossil demo

B. Instruction 1. 20-25 min. intro to Austin's geographic past, how fossils form and

show types of fossils we are likely to fmd in the creek 2. 30 min. fossil hunting

IT. Two Groups (J ust like one group except with two instructors at different parts of the creek)

A. Resource requirements 1. School Programs Fossil box

a. Two complete sets of fossils b. Two sets of charts and maps c. Two sets of clay and shells for fossil demo

B. Instruction--(Same as I B)

ITI. Three Groups (J ust like one group except with three instructors at different parts of the creek)

A .. Resource requirements 1. School Programs Fossil box

a. Three complete sets of fossils b. Three sets of charts and maps c. Three sets of clay and shells for fossil demo

B. Instruction--(Same as I B)

=Ie For more than one claSs: spread out along wall, choose different parts of creek for fossil hunting

Presentation Outline

Minerals, Rocks and Fossils (3rd-6th)

I. One Group (Three 40 min. stations-I instructor)

A. Resources 1. School Programs MRF boxes

B. Instruction 1. Mineral station and activity (see training manual) 2. Rock station and activity (see training manual) 3. Fossil station and fossil hunt (see training manual)

II. Two Groups (Three 40 min. stations-2 instructors)

*Resources and instruction are the same except two instructors rotating stations

III. Three Groups (Three 40 min. stations-3 instructors)

*Resources and instruction are the same except three instructors rotating stations

~':.".::.'.(;~.:.. ... '~

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Mineral Script

Today we are going to learn about minerals. Minerals are made up of elements.(Show Periodic Table)

Do you know the names of any elements? Examples: oxygen (in air we breathe), hydrogen, silver ,gold, copper

Minerals are made up of one or more elements. (Show and discuss letter, word and sentence IIBuilding Blocks" chart) ..

Some p;f;Ro~e made of only one mineral. (Show sulfur.) O~er minerals are made of more than one element. (Show galena-lead and sulfur)

All minerals have certain characteristics. (Show and discuss "Olaracteristics" chart)

Each mineral has certain properties that make it different from all other minerals. Sometimes geologists (scientists who study minerals) can't tell just by looking at a mineral what kind it is. Sometimes a mineral looks very different in nature. Examples: calcite, hematite

In order to properly identify minerals, geologists often have to perform certain tests. These tests identify properties of minerals. (Show and discuss ''Properties'' chart)

Today we are going to test minerals and identify them by their properties.

Procedure:

Pass out worksheets. Pass out backboards: Pass out pencils (if necessary). Tell students procedures they will use:ie. walk 'around and find minerals which fit the clues on their worksheets. . Discuss and explain worksheet Be sure to tell the students which testing equipment they will need for each item. Be sure to explain the importance of the "colorless" mineral use-items 11, 12, and 13.

After students finish the activity, go over answers. Use_ your mineral answer sheet to expand knowledge. .

Show the following samples for the it~ listed below: 1. Show pyrite nodules. 2. Show large quartz crystals. 3. 4. Show large page of mica. 5, 6. Pass galena so the students may smell the sulfur. 7. 8. Pass satin spar. 9. Pass silver-colored hematite. lO.Pass small piece of"caicite. 11.Pass mineral testing kit

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Rocks Script

Show and discuss IGNEOUS chart.

Rocks are made up of two or more minerals. There are three main types of rocks: igneous, metamorphic, and sedimentary.

All rocks were at one time igneous.

Igneous rocks are formed by volcanoes. Volcanoes are formed by magma pushing up through the earth's layers: core, mantle, and crust.

Sometimes magma cools in the veins inside the volcano. Magma that cools inside a volcano forms intrusive igneous rock. The most common type of intrusive igneous rock in this area is granite. (Show granite)

Granite is found in much of Central Texas, therefore we know that there were once many volcanoes in this area. "

Examples of old vol~oes:

Pilot Knob (near McKinney Falls State Park) Enchanted Rock is a granite dome (near Fredericksburg)

When magma comes out of a volcano it is called lava. Igneous rocks formed from lava are called ~trusive igneous rocks.' .

Extrusive igneous rocks that cool slowly have large crystals and many air pockets. An example of this is pumice. (Show pumice)

Extrusive igneous rocks that cool quickly have smaller crystals and few air pockets. An example of an extrusive igneous rock that cooled quickly is obsidian. (Show obSidian.)

Comprehension questions:

1. What forms igneous rocks? . 2. Igneous rocks formed inside volcanoes are. ____ _ 3. When magma comes out of a volcano it is called _____ ' 4. Igneous rocks formed from magma·are called ______ ' 5. What is an example of a common intrusive igneous rock in this area? 6. What is an example of an extrusive igneous rock that cooled slowly? 7. What is an example of an extrusive igneous rock that cooled quickly?

Show and discuss METAMORPHIC chart.

The next group ·of ro~ we will talk about are metamorphic rocks. "Meta" means "change". "Morphic" means "shape".

Metamorphic rocks are formed from igneous, sedimentary, and metamorphic rocks which have been exposed to heat and pressure and have changed without melting.

The heat comes from the core of tf:1e earl:tL The pressure comes from the crust of the earth.

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Some examples of metamorphic rocks and the rocks they.came from are:

Umestone becomes marble. (point out limestone and marble.) Shale becomes slate. Slate becomes schist. (Point out schist). Granite becomes gneiss. (point out granite and gneiss.)

Comprehension questions:

1. Metamorphic rocks are rocks that have been exposed to ____ and --__ -J' and have changed without ______ __

2. Where does the heat come from? 3. Where does the pressUre come from? 4. Umestone becomes ___ _ 5. Granite becomes ____ _

Show and discuss SEDIMENTARY chart.

Page 2

The last group of rocks we will talk about are sedimentary rocks. Sec:liIn.!mtary rocks are formed by weathering of igneOus, metamorphic, or sedimentarY rocks. Weathering is the . breaking down of rocks into small pieces, Weathering is caused by erosion of existing rocks by wind and water. .

After the rocks break down, the small pieces get carried by wind and water and are deposited on land or in water. These small pieces of rock a:re cemented together by minerals. 'This cementing forms sedimentary rocks.

rocks.

Many sedimentary rocks are formed in layers. (Show sandstone.) Other sedimentary rocks form around object!: (Show conglomerate.) Sedimentary rocks which form around objects are called "conglomerate" sedimentary

Limestone is the most commo~ sedimentarY rock in Austin. It is cemen~ together by calcite.

Comprehension questions:

. 1. What is weathering? . 2. Wind and water deposit weathered. material. 3. What cements sediIrientary rocks together? 4. What is a sedimentary rock that forms around objects called?

Procedure: . .

Pass out worksheets, backboards, and pencils (if necessary). Read and discuss worksheet. . Explain actiVity. Supervise as students complete activity. Go over answers. 1£ time allows, play game.

Austin Nature and Science Center

U Minerals Answer Sheet

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Find the mineral that: Write the mineral's name: 1. looks like gold ____ p .... v.r..;r_it ...... e _________ _

The nicknamefor pyrite is Fool's Gold because people sometimes think it is gold It is really sulfur and iron. It can look like gold or it can be a rusty brown color.

2. has pointed crystals ____ a .... uiiiioia=rtz ............ __ -----Quartz is made of silicon and oxygen. It can be found in igneous rocks with large pOinted crystals, in

metamorphic with small crystals, or in sedimentary chert with microscopic crystals. It is used to make glass. Some types of quartz such as amethyst, tiger eye, citrine. smoky quartz and rose quartz are used as gemstones in jewelry.

3. looks wooly or hairy (do not open) asbestos Asbestos is heatprooJ and stronger than steel, but also soft and flexible. It has been used for many things

including oven insulation, oven mitts, ceiling and floor tiles, wall insulation. but it was discovered to be a health hazard because the tiny thread-like crystals can break off, float in the air and go into a persons lungs, causing serious lung disease. 4. is thin and flaky (do not open) ___ ........;;;IDl=·;;.,;:;c.-,a ______ _

Mica, when it is formed in large sheets, is called muscovite or isinglass. It has been used to make windows for ovens, iron stoves and horse-drawn carriages. Mica can also be found as small shiny flakes in many other kinds of rocks. It is made of potassium. aluminum, silicon and oxygen.

5. is yellow and smells sulfur Sulfur is sometimes found as just sulfur, not combined with anything else. It is soft, only J % or 2 on the

hardness scale. Matches have sulfur in the tip because it burns easily. Sulfur is always found in igneous rock.

6. looks like silver and is heavy galena Galena is made of sulfur and lead. It is the most important source of lead. It is also the crystal used in a

crystal radio.

7. is magnetic magnetite Magnetite is made of iron and oxygen. It is an important source of iron. Some magnetite. callet! lodestone.

not only sticks to a magnet, but actually acts as a magnet.

8. feels smooth & slippery like a dry bar of soap talc Talc is made of magnesium, silicon and oxygen. The niclazame for talc is soapstone. It is the softest

mineral. a J on the hardness scale. Talc is always found in metamorphic rocks. It is used to make talcum powder and as a lubricant.

9. leaves a red streak on porcelain hematite Hematite is made of iron and oxygen like magnetite, but combined in a different way. It is harder, makes a

red streak and is not magnetic. The name hematite isfrom a greek word that means "blood/ike". Hematite is an important source of iron. 1 o. is shaped like a slanted cube or a slanted rectangle _____ c:;.:;a_.lc_i_te _______ _

Calcite. is made of calcium, carbon and oxygen. It is a very common mineral and is an important part of limestone and of many cave formations. Calcite is used to make cement, steel and glass.

11. is colorless and is so soft that yon can scratch it with your f"mgernail gypsum Gypsum is made of calcium, sulfur and oxygen combined with water. Gypsum is soft. having a hardness of

J ~ -2 on the hardness scale and fingernails are about 2.2. Gypsum is a very common mineral used to make plaster, cement, and wall board.

12. is colorless and so hard that you can scratch a piece of glass_Q .... u ..... a ..... rtzo..= ___ _ Quartz is being used again here. Quartz crystals have a hardness of7 and glass is 5.5.

13. is colorless and is too hard to scratch with your f"mgernail and too soft to scratch the glass calcite

Calcite is being used again here. Calcite crystals are a hardness of 3, fingernails are 2.2 and glass is 5.5.

u Austin Nature and Science Center

Rocks

Find the rock that: Write the rock's name:

1. A sedimentary rock that is gray with wavy markings .;;;li..,m_.,,e .... soiioito ... D ... e ________ _ Limestone is the most common rockfound in Austin. It isformed in layers under the ocean. Some limestones are hard and grey, some are softer and some are white, or a pale yellow or pink. 2. A metamorphic rock with different colored stripes agD-.-ei ... s-...s ________ _ Gneiss is rock that almost melted and stretched like taffy. This gneiss is from the Hill Country near Inks Lake and is over one billion years old. 3. An igneous rock with dark blue crystals ._1l,..a ... Dl .. ·t,;;..e _______ _ Llanite is a type of granite with blue quartz crystals. It is only found near Llano, Texas and is also about one billion years old. 4. A sedimentary rock that could write like chalk ... ch .... al .......... k _________ ......---Chalk is a soft form of limestone. Today people make chalk, but long ago chalk rocks were used on smooth pieces of slate in

classrooms. 5. An igneous rock that is light and floats in water ... PoiiiioU=IDl ... ·c ..... e ________ _ Pumice is froth from a volcano. It floats because many air bubbles are trapped in it. Pumice is sold in drug stores to use in the bathtub to smooth calluses from feet. 6. A metamorphic rock with very small shiny mica flakes .... sciiioiiih ... is __ t _______ _ Schist is rock that melted even more than gneiss. This schist is very, very old, some of the oldest rock on earth. It is as old as the rock at the bottom of the Grand Canyon. It comesfrom the Hill Country near Llano, Texas. 7. A sedimentary rock made up of different sized pebbles conglomerate Conglomerate is formed from sediments of gravel that become cemented together.

U. An igneous rock made up of pink, clear and black minerals .ag.-ran=iioiiote _________ ---Granite is an important rock for building. This Texas pink granite was used to build the State Capitol building. It is found near Marble Falls, Tx and at Enchanted Rock. It is also about one billion years old. 9. A sedimentary rock that looks like layers of sand _sa;;::n::.;;d_s_.to_n::.;;e ________ _ Sandstone is formed from sediments of sand that become cemented together. It can be golden, red, gray, even green. Green sandstone can be found near Lake Buchanan. 10. A sedimentary rock that has finger-sized holes .,.k ..... ar __ s ..... t _______ _ Karst is aform oflimestone. It is the rock thatforms the Edward's Aquifer, a large underground areafllledwith water that is the source of water for Barton Springs andfor much of San Antonio. 11. An igneous rock that looks like black glass .-,ob_s_i.-di_· a=n~ _________ _ Obsidian is glass that is made in nature from lava that cooled very quickly. It was used for tools by native people because it breaks to a very sharp edge, but it isn't very strong at all because it is basically glass. 12. A metamorphic rock that is white and smooth .;;;m=a_r.;:;b.::.;le _________ _ Marble is used in buildings and for sculpture. Marble comes in many different colors. White marble like this is what Elisabet Ney used to make her sculptures that are in the State Capitol building. 13. An igneous rock that is dark with small holes; feels rough ._,b.-,as::.;;a;;:;lt _________ _ Basalt is basically just cooled lava from a volcano.

14. A sedimentary rock that is brown and feels slick. It has sharp edges and was used by Native Americans to make tools. chert

~~----------------Chert is also called ''flint''. It is made of microscopic crystals of quartz. Chert was used by native people to make arrowheads and knives. It makes a stronger tool than obsidian, so it was used more often.

Extra: What is the texture of each of these rocks? Circle the ODe you choose. Limestone A. glassy B. fme-grained C. medium-grained D. coarse-grained Granite A. glassy B. fine-grained C. medium-grained D. coarse-graiDed Obsidian A. glassy B. fine-grained C. medium-grained D. coarse-grained

U Sandstone A. glassy B. fine-grained C. medium-grained D. coarse-grained Conglomerate A. glassy B. fine-grained C. medium-grained D. coarse-grained

Gneiss A. glassy B. fine-grained C. medium-grained D. coarse-grained

u ROCKS-

1-Rocles are the •••••••• lI'eet, of the elrth. 2-Tbay Ire composed of one Dr more •••• ,.. ••. 3-They tIn be ••• 11 grlln. or " •• e, •• II~ or In I •• It •• stete.

WORDS USED IN THE •• CIC TI'E MATCHING GRME

IEI.MENTI.' Limestone Conglomerate Sandstone Layen Erosion Deposit

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Sldlmlnts stert when roct. breat down, and the pieces are clrrled .by wind Ind wlter (E •• II.N ) Ind IEPIIITEI In LIIEIS, with the youngest on the top. .

Sldlmentl'll gets farm when sediments (lilee slInd or mud) are U cemented togetblr with minerai, ,ueb .1 colclte lod 1lllco.

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S •• ~st ••• Is cemented Sind, LI ••• t ••• Is cemented shells, timely mud I Ind cllclte. 5".'a II cemented mud C •• ,I ••• ,.ta roctl hlUI a mlHture of different IIz8 rocts

cemented together- (Sind size Ind gl1luel size) .

MElIM ••••• t 6neisl Schist Marbl. 51,t, Heet/pressura Chenge

Metamorphic rocles are rocks that haue been aRposad to 1I •• t •• ~ .re ••• n and e ........ without melting (the minerals and the composition change). Note: Once they malt thay Ire mogml.

Llmestonl turns Into •• nla Mudstone or shlle turns Into I'.'e, schist or , ••• 11 depending

on bow much heat andlor pressure they wera 8Hpoled ta, Igneous rocts mey tum Into •• a.s. Sindstonl turns Into ••• rtzlte

IINE •• S

Magma Granite Llue Intrullus EHtrullus lIolelno

'gnsous rocks ore rocks that ore or were melted. Molten or melted rock Is called •••••• I f It comes out of I

•• Ie ••• It Is celled •••• , Ind II considered ID •• Ir ••••• roct. (eHlt­out). Pumice Is laul with Ilr bubble. In It, Ind oblldlon II IluI thlt cooled so fa.t thl Crystl'S didn't hlue tlml to form Ind II considered uoleanle glass.

MolteD roct thlt doesn't get to the surflce Ind Insteld cools underground Ira considered •• tnl ••• rock (In • Inllde). 1,...lte Is one of the mllin Intruslus roctl we find, Ind the IlIrge crystlls tell ~s n a long cooling procell. Remember. thl Imilier the crystlll, the flster the coollng- Ind the larger the cryltlll tha-Ionglrthe coDling time.

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SEIIMENTS INI .ICES (bactlrounll infe)

The elrth Ind auerythlng In It Ind on It, lIulng or non- lIulng WIS mlde Inside .. stir which eHploded (supemoul) more thin 4 1/2 billion years Igo. The elements which mllee up euerythlng were crelted inside of it while It WIS I 'shining star (III the alamants up to Iron), or when it aHplodad (the lass common beluy alemants'. The sun, pllnets, 81rth Ind III of UI Ire -st.r .... t -•

RII rocks on elrth orlglnilly started II •• , •• It some time In earth's history •

••• t ... rI •• -When rockl Ire eMpoled to the elements they brelk down, alther by physlca. chlng.1 luch IS heating Ind cooling, or by chemicil chlnge. clused by Interlctlons of the rockl, weter, lind chemlclls In the enulronment.

Erall ...... ".,.III ••• -Rfter the rockl break down, the mlterlals gets carried by wind Ind wlter (.,..s ••• ) Ind 1I ..... lt.~, on lend or in water., Materials Ire deposited In ••• en- the youngest II It the top.

SEDIMENTS ROCKS MRGMR SEI.MENU.'

LIISE CINSll.lm. MOl ....... 1£ MELTEI (glued 1111 minerai.) (helt + pre.ure.

thlnged without melting

LI~EY MUD LIMESTONE MARBLE MRGMR .mln Inimllsbell. and celt". ClIY SHILE SLRTE 15tH I ST I&NE I 55 MRGMR mlnerelt ,It.t 'Gnawhaa Ignea_net •

. breltda •• SRND SANDSTONE QURRTZITE MR6MR the quartz grain. len wilen Igneou. roca Dreat down 6RRUEl CON&lOMERRTE GNEISS MRGMR roetl If different lize ... II ."ape. delendlng on Whether fre,Ia or .tn ... WDrn

MIS .... TlINS INTI •• CIC _lEN IT CIILS.

The wig I gneDus rocks loot dependl upon tbe minerals Dresent. and the cooling rote.

I gn80us rock thlt Is cooled '"t (I ••• ), hiS smlll crystlll end I fine grain. 1 •• llt. and •••• 11. (E.lr •• I •• I' ••••• r.ct.)

I goeous rock that eOQls lie", slowlU underground hll Ilrge crystals and allrge grain. lna.lt. and •••• ra. (I.tnl ••• I •••••• nets'

Dolcenit rock that Is cooled uerg fast mey be ... ,111 ••• (uolclnle glass) or .... Ic. (If air bubblel In It). Both Ire cooled 10 fa.t thlt no crystlls form.

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MINERIlS -Cbaracteristics: 1- Made up of one or more chemical element. 2- Non-Iluing 3- Found In nature (naturally occurring) 4- E8th mineral alway. he. tbe seme elementl In the seme arrangement (the same through and through). 5- There is an orderly arrangement of atoms (repeating pattems)­which forms crystals In chlrlcterlstlc shIpes (not III specimens of I miner.' will show crustlilioe form, but DO I Itomlc leuel the arrangement II the same).

Compare minerals and laDluage: 1- Elaments • letters (there ar 92 elements Including slluer, gold, copper, iron, clrbon, - cln be gesses ella such .1 Hydrogen and OHygen) 2- 'Mlnlmls • words (You cln ule lama letters to maka different words. Minerals sometime. hlue s.ma elements In different arrangement Ind the m.lnerel. will heue different properties and different nlmes). R few simple eHamples of minerals: Silica + ONygeo • Quartz (5102)1 Hydrogen + OHygen • Water (H20) I I ron + Sulfur· Pyrite (F eS2) 3- Rocks =: sentence. 4- Stroto • paragraphs S- FormatlDnS • chapters

IIENTIFICRTIIN IF MINERllS-properties R minerel, whlt.Der it' size, whether crystalline or masstue, hiS properties.

Some 8Hlmples of properties: ·crystals (square, pOinted, fit, needlelike) *eolor (,.ml mlnarll mly comlln different colon - quartz.) ·hardness *CIBlulge (breale 810ng I plene of weak atomic bonds) *fracture (Irregular break) ·strellc *welght (spectfle grtlulty- or lilt heDDY or light for Its size) ·does It fizz If you put acid on It ·magnetic ·smell ·Iuster

M I NEilL DETECTI DES FIN. TIE MINERll TIlT MITCIES TIE CLUE (property) end write It, name In the blank.

-I n the center of the circle pllce: *gllss to te.t for hirdnesl *8 porceilin pllte for scratch test *megnet for megnetlsm test *other tools Include, flngernell, eyes, sense of smell and touch

-Tell the students: ·geme II not I test *mlY ule the .Ime minerll mora then anI time *mlY Isk que.tlonl *mey shire Informltlon *1.I.,e the specimen on Its nllme cerd (alt If you·re not sure) *don't open the albestos container plel •• *try to determine herdness with IS few scratches on the gillS In

pos.lble

- Wllk Iround the circle end say Ibe minerai·, nomes.

- Heue tbe students walt tbe eirele to lei all the IDeelmao ••

- 61ue the students the go ahead to became mlnerDI detectlues.

-FINIL •• 1'-1' - 60 ouer the Inswen and tell Interesting In10-

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BACKGROUND INFORMATION ON GEOLOGY OF THE EARTH AND OF TEXAS

COMMON TEXAS ROCKS

Cf)

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ROCX '''AUMENTS. CGIoIMOHL' 'OOIt IEDOINII:Dt:~SIn:D IT JlUNNrNG WATE" •• 'ND. OR ICE

I -tit 0 Q L&J I en 8 til • a ~

~ til Z

= INTENSE HEAT DAIIIC AND LIGHT IAHOS.CUfWED FQL.ATlOHSfSCHlSTOSITYI.CI' SLAn CLU'lAGE

MAY MELT ~------------------------------------------~SE~MENTARY~--------------------------------------------~

UNCONSOLIDATED SEDIMENTS ItOCICS AND METAMORPHIC ROCKS ~--------~----------------------~--------~ 'UIE THEM ~------~---.~------~----------------------~

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OItANrTE

WUTHEIUNG AND nOllON l"UIe DOWN IGNEOUS AND IIUAMOM'HIC IIOCICS TO '01111

UNCONSOLIDATED SEDIMENTARY

DEPOSITS

OIlANULAIt "OCKS

"HYOLln

liTO

TItACHYTE 'EUIT!

INTI_teAT. ~ • .uct va~OIts. COMUONL' 'JlOM DEE""" BUlliED ra·

NtOUS AOOlS. May ItECIt'fSTALUU .. TAIIIIOfIAtC ROOCS ,~ lEW

FIC. 18. Sketch showing the relationships of the three general kinds of Texas rocks.

, ,

~ CRUST dna MANTLE (rocky) --<.-----­Mesosphere. solid Asthenosphere, partly molten Lithosphere. solid

The Earth has not always been as we see it today, and it is changing (but slowly) be­fore our eyes. The highest mountains are built of materials that once lay beneath the oceans. Fossil remains of animals that swarmed the seas millions of years ago are now dug from lofty crags. Every continent is partially covered with sed­iments that were once laid down on the ocean floor, evidence of an intermittent rising and settling of the Earth's surface. (3)

. Earth Volume, Density, and Mus

Av. Volume, Mean thickness or . millions density, Mass. radius. km of km~ Q/cm3 x 1(}14 g

CORE (meTdllic) Inner core 1 solid outer core. molten

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LUJlcs;lh.,. ( I i

AlUlaIO&;Ih_ < Total earth 6.371 1.083,230 5.52 5.976 i Oceans and seas 3.8 1.370 1.03 1.41 l

~ __ --1I!1:

Glaciers 1.6 25 0.9 0.023 1.10 The reletiOJWu;ll between the UPJ)e1' mantle and CNIt (contmensaJ and oceofUc:1 ana @ Continental crust 35 6.210 2.8 17.39 the lilho.phere and aatheftOl1)here. (See aIIo FII;we 10.28.1

Oceanic crus I 8 2.660 2.9 7.71 Mantle 2.883 899.000 4.5 4.068 Core 3.471 175.500 10.71 1.881

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. . IGNEOUS ROCIS

Satellite cone -.-----:,; ....

3.20 Plutons and landforms associ· ated with igneous activity.

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Maqma reservoir-

Igneous rocks are formed from the solidification of molten matter.

Igneous activity consists of movements of molten rock inside and outside the eanh and the variety of effects associated with these movements.

Cause of igneous activity seems to be the same internal force that elevates mountains. causes earthquakes. and causes metamorphism .

The Eartb's beat is indicated by the thermal gradient to be more than adequate for igneous activity. Speculations on tbe origin olthe Eanb's beat have included original heat and radioactiv­ity .

Ipeous rocks at the surface today were fonned from magma. Magma solidifies through the process of crystallization. BoweD's reactioD series are incorporated in a hypothesis accounting for all igneous rocks conung from an olivine basaltic magma.

Limitations of BoweD's hypothesis include failure to account for large undifferentiated masses of granite. The rate of crystalUzatiOD is an imponant control over the rocks that fonn.

Texture of ipeous rocks is determined by the size. shape. and arrangement of their interlocking mineral grains. .

Gr:muJar texture includes large mineral grains from slow<ooling or low-viscosity magma. Aphanitic texture from rapid cooling consists of individual minerals so small that they cannot be identified without the aid of a microscope. Glassy texture results from ions disorganized as in a liquid but frozen in place by quick cooling. Porphyritic: texture is a mixture of large mineral grains in an aphanitic or glassy groundmass. Pegmatitic texture is an exceptionally large granular mass of crystals formed by hydrothermal solutions late in the cooling of a magma. .

Types of ipeo1ll rock are arbitrarily defined in terms of texture and composition. Dark-c:olored ilDeous rocks (intrusive grabbros, extrusive basalts) constitute 98 percent of rock fonned from magma that has poured out onto the Earth's surface. Intermediate types of composition are given arbitrary names, such as 8Ddesfte and diorite, because igneous rock compositions blend continuously from ODe to another from the dark to the light side of the classification chart. Ligbt-colored IlDeoa rocks, sometimes called siaUc, are dominated by granites and gnmodio­rites.

Qriam of magmas varies from partial melting of portions of the lower crust and upper mantle that produces primary magmas, to fractional crystallization or other changes that result in s~on~ma~. .

Three primary magmas are basaltic, granitic, and andesitie.

Relationship of magmas to tectonic: settin81 is demonstrated by different magmas occurring at di1f'erent plate boundaries.

Masses of igneous rocks are called plutoDS, which are classified according to size. shape. and relationships to surrounding rocks.

Sills are concordant tabular plutons. Dikes are cUscordant tabular plutons. Lopoliths are tabular concordant plutons shaped like a spoon. Laccoliths are massive concordant plutons with domed tops. Batholiths are massive discordant plutons 10 to 1S km thick.

• ..... 'aIIlUI ,.IIlIe t10CKS

'nCt .... 'n ,n,.n,,,y 0' ...... '" to""/11

METAMORPHISM OF SHALE

SHALE Clay "'1ftet8II

f SLArE

CIIY m'nelll' Deq,n 10 'ectytlllhl.,n,o .... ICI'OICOOIC m'CI 9ra,nl wnlcn oroauc:.

SlalY Cl.av191

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MIca CIVIIIII GlOW .. rv_ '''a 101'" CO"IDICUOUI

'Ollillon

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ORIQINAL ROCK Low •• mOlrall.lte Meckulft telftDeralure H'9" "/IIDe,.,,,,. Ina Ol"'UI, anD ore •• url .na DrtUu ••

SHALE---~ SLATE

AHYOUTE ORAHITE

Gr_ 01 ""croICOD'C: m,CI

BASALT .-...---------1

SCHIST GroWln ol.tfIJl mlCl

9'1'''' O,vl Guam I"C! DO • .,O.y 'e'OIDI'. 911"".

tll:ller.

GNEISS t

Lne,. 01 ' .. a.ol' ; GUlrtZ. Ina "''''0' ""ca. I 9Ir" ••.• no l"'onIDa,. .

.u.CPH'BOl.lTE COII"'9I1'"'O I"'DnlDOle.

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Figure 7.7 The metamorphism of shale. @

UMESTONE---~

5AHDSTOHE----~

MARBLE LIIQ' cryattl. 01 CIIC'" or aO'olll'"

OIUI m'nOl ',"DUll""

OUARTZITE OUI"Z D'u. m'no, '/IIOU''''''

We can never observe metamorphic processes in action because they occur deep within the crust. but we can study in the laboratory how a mineral reacts to high temperatures and pressures that simulate. to some extent. the metamorphic process. These laboratory studies. together with field observations and studies of texture and composition. provide the rationale for interpreting metamorphic rocks. Figure 7.6 Generalized chart showmg the orlgm at some ~

of the common metamorphic rocks. ~

Metamorphism produces metamorphic rocks by changing i8neous and sedimentary (and other ~ metamorphic) rocks while they an: in the solid state. ~

Agents of metamorphism are heat, pressure. and chemically active fluids. Heat may be the essential agent. Pressure may be great enough to induce plastic deformation. n ChemicaUy actiYe fluids, particularly those released late in the solidification ·of magma, react on surrounding rocks.

Types of metamorpiJism are contact and regional. Contact met:lllDorphism occurs at or near an intrusive body of magma.

CoDtaet metamorphic: miDerais include wollastonite, diopsicie, and some oxides and sulfides constituting ore minerals.

RegioD81 metamorphism is developed over extensive areas and is related to the formation of some mountain ranges.

Regicmal metamorphic facies is an· assemblage of mhleraJs that reached equilibrium during metamorphism under a specific set of conditions. Regional metamorphic minerals include sillimanite, kyauitc, andalusite, staurolite. almandite garnet, brown biotite, epidote. and chlorite. . RegioDal metamorphic zones are identified by diagnostic index minerals.

Metamorphic rocks are found in m~UDtain ranges, at mountain roots. and on continental shields.

Textures of metamorphic rocks are nonfoliated and foliated. NoDfoJiated rocks do not exhibit rock cleavage. Foliated rocks exhibit rock cleavage as slaty, phyllitic, schistose, or gneissic.

Metamorphism and plate boundaries are closely related. Conyergent boundaries show increased temperature and pressure effects on subducting slabs of lithosphere with sedimenis intruded by batholiths, downwarped thick sedimentary se­quences, and plates that have collided. Di\'ergent boundaries have bigh heat flow at spreading centers with mineralization including sulfides and evaporites. Transform or parallel boundaries have less igneous activity but include some metamorphism and some economic mineralization.

Granitization \'5. Metasomatism refers to the debate over what percentage of the world's granite is produced by each of these processes.

Geothermometers are animal, plant. or !!lineral indicators of changes in the earth's temperature.

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SEDIMENTARY ROCKS

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~ III 1\1 ~ f iii 0 E 1:1 iii

CI III ~ 0 a: g .5 E iii Q. III 0

"-III 0 'C rn 1:1 ~ U Q.

III III ~ W C ~ Ci. ~ III U Q 'iii 1:1 2 III

CI 1/1

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£. iii 1/1 ~ 1:1 E .:. c

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E 0 c: III D Iii ·iii 0 1'0 1; ii 1/1

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III CL

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W

W t-

W W < W Z Z z a:: z w 0 0 w 0 w 0

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Alluvial fans

Dunes (eolian)

Playa lake

@ Sedimentary rocks cover about 7S percent of the Earth's surface and make up about 5 percent by volume of the outer 10 km of the solid Eanh.

Formation of sedimentary rocks takes place at or ncar the Earth's surface. Detrital material worn from the landmasses and chemical deposits precipitated from solution arc the two chief types of sediments. Sedimentation is the process by which rock·fonning materials arc laid down; the resulting deposits vary with the source of material, the methods of transponation, thc processes of deposition, and the environment of deposition. Clay, quartz. calcite and some feldspars are the most common minerals in sedimentary rocks. Other minerals include dolomite. goethite. hematite. limonite. mica. halite. and gypsum. Texture depends on the size. shape. and arrangement of the panicles. T exturc may be Ciasllc or nonclastic. Diaaenesis includes all the physical. chemical and biolo~ical chan~es that occur afler burial but prior to or immediately following lithification. Lithification convens unconsolidated sediments to firm rock by cementation. compaction. desiccation. crystallization.

Types of sedimentary rocks include detrital. chemical. and biochemical fonns. Detrital rocks include conglomerate. sandstone. siltstone. and mudrock. Chemical rocks include limestone, dolostone. and evaporites. Biochemical rocks include chalk. coquina. diatomite. coal, and some limestones. Most abundant are shale and mudstone. sandstone. and limestone. in that order. Thev form 99 percent of the sedimentary rock family. .

Features of sedimentary rocks include bedding. mud cracks. nodules. concretions. geodes. and fossils.

Color of sedimentary rocks is due largely to small amounts of the iron oxidc minerals and. less imponantly. to organic matter. Sedimentary facies refers to an accumulation of deposits that exhibits specific characteristics and that grades laterally into other accumulations formed at the same time but showing different characteristics.

Sedimentation is closely related to plate boundaries. with thick accumulations along some margins.

Glacial Fluvial

Lagoon Beach Delta

Tidal flat

oon

Organic reef

Figure 6.13 Schematic diagram showing the major '2:'" environments of sedimentation. ~

)

Geolo2ic Time Scale

Epoch Millions Millions Charac- ·Whae _ of Years of Years eeriseic Happened

Era Ago Period Ago Life in Ausein ~-.~ .. =~~~======~~~-=~~~-.. ~ .. ~-~.-~--~~~-,,-; Archeozoic --Pioterozo~c 4000-600

It

Paleozoic 600-255

Mesozoic 250-65

Cenozoic 65-0 Paleocene Eocene Oligocene Miocene Pliocene Pleistocene Recent

Pre-Cambrian

Cambrian

Ordovician

Silurian

Devonian

Mississippian

Pennsylvanian

Permiau

Triassic

Jurassic

Cretaceous

Tertiary

Quaternary

Bacteria Jelly Fish Corals Algae

600-500 Trilobites,

500-425

Molluscs

First Vertebrates

425-405 First Land Animals Spiders. Scorpions

405-350 Primitive

350-315

315-285

Fish. First Land Plants

First Amphib ians • Spore-Bearing Plants

First Reptiles. First Trees

285-230 Reptiles in Texas. Age 0·£ Dinosaurs Begins

230-180 First

180-135 First Birds

135-65 First

65-1

1-0

Flowers. Dinosaurs Become Extinct

First Primates, First Grasses

Ice Age-Man

Llano region granites, rhyolites and metamorphic rock

Shallow, warm sea covers the area

Limestone forming

Deposits of coal accumulating

Ouachita Mountains formed, sea retreats westward

, Ouachita Mountains sank

Sea advances and retreats from gulf

Volcanic activity Llano Uplift

Sea retreats to Balcones Fault (15-25 million years ago

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Glossary

. spite of aU efforts to avoid using specialized jargon. a few such J appear in this book. Perhaps this glossary wtll help the reader.

Algae. Primitive seaweeci: one of the first forms of life. Alluvium. A deposIt oi sand or mud fonned by flowing water. Anhvdrite. Llterallv, without water. Specifically, a sulfate of cal­

cium d~posited when ~lneral-rich water evaporates. Gypsum with­out the water.

Arch. An upward bending of rock layers. Ash. Residue from burning. Geologically, fine particles of crystal­

lised silica from a volcano. Basalt. A dark colored volcanic rock. The most commonly seen

type of lava. Batholith. A large body of igneous rock. that intruded older rocks

and solidified far below the Earth's surface. Calcite. Calcium carbonate. One of the most common rocks and a

major constituent of sea shells. Generally deposited by sea-water as limestone.

Cambrian. The oldest geological period of which we have fossil record. The name derives from Cambria or Wales, and it includes the time from some 700 to 500 million years ago.

Carboniferous. Literally. the time of coal. That part of geologic time from 330 to 270 million years ago when tree-like plants were the dominant fonn ofUfe. The Mississippian and Pennsylvanian periods.

Cenozoic. The geologic era coverIng the most recent 80 million years and including the Tertiary and Quaternary epochs. From the Greek words meaning common or now-known life.

Chert. A compact sedimentary rock consisting primarily of quartz without evident crystalline fonn.

Conglomerate. A sedimentary rock composed of gravel or boulder size rock fragments deposited by moving currents of water.

Cretaceous. The geological period extending from about 140 to 80 m; ":.,n years ago. Limestone is the dominant rock type as is implied t : name from the Latin for "chalk."

Crust. The rigid outer part of the Earth generally extending to a depth of about 60 miles 1100 km. J.

Delta. The muds and sands deposited by a river where it reaches the sea. So-called because of its common roughly triangular shape.

Devonian. The middle pan of the Paleozoic Era extending for about 70 million years, from about 400 million years ago. Named for its wide-spread exposure in the Devon area of England.

Dike. A generally narrow and elongate body of igneous rock fonned when magma was squeezed into a fracture zone.

Eocene. The period of Tertiary time between about SO and 40 . million years ago. Literally "dawn of recent".

Evaporite. A 28dimentary rock composed ofmineraJs such as salt and gypsum which result from the evaporation of salt water.

Extrusive. An igneous rock, such as lava. which formed when magma spread out and cooled on the Earth's surface.

Fault. A fracture in the Earth's crust separating blocks that shifted past each other. Commonly distinguished because the rocks on the either side do not match.

Flint. Similar to chert, but commonly occuring in nodules. Its extreme hardness and flaky fracture made it a favorite for arrow points. axes. etc. .

Fossil. Any remains or trace of an animal or plant that lived in the geologic past, as a shell. skeleton. leaf impression or foot-print.

Glacial. Pertaining to or caused by moving ice sheets. Generally used to describe the great continental glaciers that covered much of the Earth's surface during the Pleistocene period from about 3 to 1 million years ago.

Gneiss. A common metamorphic rock composed of re-fonned min­eral crystals. Somewhat resembles a streaky granite. Pronounced "nice". .

Co \te. An igneous rock composed of quartz and feldspar with . son. rk minerals. Generally grey to pink in color. U Gypsum. An evaporite composed of calcium sulfate and water. .. Hiatus. A gap in the geologic record: an unconformity.

Hornblende. A shiny black or dark green mineral common in most igneous and metamorphic rocks.

Ice Age. Any time characterized by major glaciers. Generallv used for the Pleistocene period. .

Igneous. Any rock that has solidified from a molten state. From the latin for fire.

Inlier. An outcrop of older rocks completely surrounded bv younger rocks. .

Intrusive. An igneous rock that solidified when the magma crys. tallized below the surface.

Jurassic. The geologic period from about 180 to 140 million years ago. Named Cor the Jura Alps in Europe.

Lava. The hardened rock which flowed from a volcano. Limestone. A sedimentary rock formed largely of calcium carbo.

nate. Commonly contains marine fossils. Lithology. The science dealing with rocks, and thus the physical

and chemical characteristics of rocks. Magma. Any molten rock. Marl. An impure limestone or a limy clay. Mesozoic. The geologic era between the Paleozoic and the

Cenezoic and including the Triassic, Jurassic and Cretaceous. It includes the time from about 250 to 80 million years ago. The name means middle life. In older literature it is called "Secondary".

Metamorphic. Changed in form: thus rock whose character has been altered as by heat and pressure.

Mica. A common mineral in igneous and metamorphic rock. It may vary from white to black. but always splits easily into thin flat flakes or booklets.

MiDeral. The inorganic erystals or fragments of which rocks are formeci.

Miocene. That part of the Tertiary period extending from about 25 to 11 million years ago. Literally "88S recent".

Mississippian. The oldest part of the Carboniferous period of the middle Paleozoic. Named from its wide exposure in Mississippi. and in Texas considered as the youngest part of the lower Paleozoic or as the time of transition from lower to upper Paleozoic. About 330 to 300 million years old.

Normal Fault. A fracture in the Earth's crust caused primarily by a pulling apart of the ·rock due to subsiding caused by gravity.

OllgoceDe. The middle part of the Tertiary epoch extending from about 40 to 25 million years ago. The name means that few modern life forms were then existent.

Orodovician. The lower Paleozoic period from about 500 to 400 million years ago. Named from an ancient British tribe in northern Wales; a time of widespread limestone-depositing seas in Texas.

Outlier. An erosional remnant of younger rocks perched on· older rocks.

Overthrust. A fault or fracture where older rocks are pushed up and over younger rocks. A thrust fault.

Paleozoic. Literally "old life".The time when recognizable fonns of life first appeared on Earth from about 600 to 250 million years ago. Sometimes called "Primary".

Pegmatite. A coarse grained fonn of gnmite having crystals at least an inch (2.5 em.) across; almost always occurs as dikes. Often a good place to collect mineral specimens.

Pennsylvanian. The part of the Paleozoic time between the Mis­sissipPIan and the Permian. or between about 300 and 270 million years ago.

Penman. The youngest period of Paleozoic time. between abut :!iO and 250 mi Ilion years ago.

Pleistocene. The earliest pan of Quaternary time from about 3 to 1 million years ago. ORen called the Glacial or Ice Age. Literally tr near recent".

Pliocene. The youngest part of Tertiary time or about 10 million to 3 million years ago. Literally "more recent".

Precambrian. The interval of time between the age of the oldest known rocks - about 4 billion years - and the start of Cambrian time about 600 million years ago.

Quartz. One of the moSt common minerals in most rocks, wnetller igneous or sedimentary. Silicon dioxide.

Quaternary. All time since the Tertiary ended about 3 million years ago.

Tertiary. The interval of time between the end 01: the Cret:lCeol' • about 130 million vears ago and the bespnnmg of the QU~lernar\' about 3 million ::~ars ago. .

Radiometric. Referring to the measurement of the changes in elements by the los8 of radiant energy. Widely used in estimating the age of rocks.

Thrust Fault. A fracture In the Earth's crust whe' ier -have been pushP.d over younger rocks. ~

Triassic. The interval of time between the end of the P:lI l: Recent. The last million vears or so of the Earth's history. Rhyolite. A light colored ~'ariety of volcanic rock often including

volcanic ash.

about 250 million years ago and the start of the Jurassic about L"O million years ago.

Rock. Any naturally occUlTing. but i~organic. combination of minerals.

Sandstone. A sedimentary rock originally deposited as sand. The individual grains can generally be seen.

Unconformity. The contact between two or more well deiined sequences of rocks where a significant time interval elapsed. Com­monlyaccompanied by erosion and perhaps tilting of the aider rocks before deposition of the younger.

Schist. A common metamorphic rock with a streaky or layered appearance caused by the presence of mica.

Unconsolidated. Loose sedimentary material not hardened or cemented into solid rock.

Sediment. Any natural material that has been transported and deposi ted by water or wind.

Valley Fill. Sedimentary material such as gravel. aand or mud deposited in a valley.

Shale. A very fine grained sedimentary rock deposited in rela­tively thin layers.

Vein. Any milleral deposit that fills a fracture in older rocks. May be either igneous or sedimentary.

Silica. Silicon dioxide or quartz in its many forms. Weathering. The various surface processes that break up or de­

compose solid rock to fonn soil. Siltstone. A sedimentary rock with grains too coarse to be shale or

clav, and too fine to be sandstone. Silurian. That part of Paleozoic: time between the Ordovocian and

the Devonian or about 440 to 400 million years ago. Stock. A small intrusion of igneous rock: often the solidified core of

a volcano. Tectonic. Referring to the forces or conditions within the Earth

which cause movements of the crust ranging from minor faults to the building of mountain ranges.

BOX 10.2 List of the twentieth century's most deadly natural disasters ®

This list of the twentieth-century natural disasters that have caused more than 10.000 d~ths shows that a very large proportion have been associated with earthquakes.

Estimated Deaths

• 3.7 million-flood of Yellow River in China. 1931

• 6S5.000--earthquake in Tangshan, China. 1976

• SOO,OOO-<:ycione. tidal wave in Bangladesh. 1970

• 200.000-ftoods in China, 1939

• 180.000--earthquake. landslides in Gansu. China. 1920

• 160.000--earthquake in Messina, Sicily. 1908

• I 43.000--eanhquake, fire in Tokyo­Yokohama. Japan. 1923 .

• 100.000-ftoods in North Vietnam, 1971

Mochfied from Los Angeles Times, May 28. 1985.

• l00.000--carthquake in Gansu. China, 1927

• lOO,OOO-flood in Canton. China. 1915

• 70.000--earthquake in Gansu, China, 1932

• 66,794--earthqua~e in Yungay, Peru, 1970

• 57,OOD-flood of Yangtze River in China, 1949

• S6.000--earthquake in Quetta, India, 1935

• SO,OOO-tidal wave in Italy. 1908

• 50,OOO-earthquake in Cbile, 1939

• 50,OOO-earthquake in Turkey. 1939

• 50,OOG-ftood of Yellow River in China, 1933

• 4O,OOO-volcano eruptions in Marti­nique, 1902

• 4O,OOO-cycione in Bengal, India, 1942

• 4O.~ood of Yangtze River in China, 1954

• 30,OOO-earthquake in A vezzano, Italy, 1915

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• 30.000-ftood of Y c:llow. Yangtze rivers in China, 1935

• 2S.~rthquakes in northeast Iran. 1978

• 24.047--cycloncs. tidal waves in East Pakistan, 1965

• 23,OOO-mudflo.ws from volcanic eruption. Nevada del Ruii Colombia. 1985

• 22,778-earthquake in Guatemala. 1976

• 22.000-storm in Chittagong. E. Pakistan. 1963

• 19,()()()..-...earthquake. flood in Kangra, India, 1905

• 15,()()()-cold in Inner Mongolia and Suiyuan, China, 1930

• 14,OOO-earthquakes in Central Asia. 1907

• 12.2()()..-earthquake in Guatemala. 1902

• 12.000-eanhquake in I ran, 1968

n 10.6 Interpreting Earthquakes 1 '1 ~

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Cenozcic [D River deposits

• Sandy -muddy sediment,

Mesozoic [~ Chalk and clay

m Umestone and sandstone

.. Umestane. sandstone. and shale

Precambrian E:] Granite and related rock

Table 1. GeologiC age Ind duration of the major subdivisions ler.sl of geologiC: time

(numbers indicate millions of vears before present).

Name of era Time span

Cenozoic: 70 to present

Mesozoic· 225 to 70

Paleozoic 600 to 225

Precambrian Prior to 600

-The CtelllC»OUl Period is Pin of the Mesozoic era ulendlRlI about 135 to 70 million vear, before pre_tn. DUring IhlS lime IOCkl d the Hili Counvv anet the inn8f' Gulf Coast.1 ~In were forr

i. Generalized geologic map of the CAPCO region (modified from Darton and others, 1937).

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GEOLOGY OF CENTRAL TEXAS

The material in this handout is copied from the books listed in the

references. I have attempted to give some background information so that

the context in which the landforms we see can be understood, both how and

why they were originally created, and why they look the way they do now.

Each picture or statement from one of these books has a number in a circle

which corresponds to the reference so that credit is: given where credit is due.

This journey will cover geologic formations tha~:span an enormous

amount of time and a great var1ety of processes. I hope everyone returns

with an increased understanding and some wonderful memories.'

REFERENCES

1- ENCHANTED ROCK - A NATURAL AREA SURVEY NO. 14 by the Lyndon B.

Johnson School of Public Affairs. The University'of Texas at Austin. 1979.

This wonderful volume is not available' for sale but can be found in some libraries.

Textbooks:

2- THE EARTH'S DYNAMIC SYSTEMS by W. Kenneth Hamblin ~('~2nd'edition,1978)

There are more current editions of this book available. I love the photographs and diagrams in this book and the text is excellent and informative.

3- PHYSICAL GEOLOGY by Sheldon Judson, Marvin Kauffman, and L. Don Leet

( 7th edition,1987 )

This is the text used in the Physical Geology course I took. The illust~ations are beautiful and the text clear.

Popular Geology booksl

4- PAGES OF STONE- GEOLOGY OF WESTERN NATIONAL PARIS AND MONUMENTS - #3- The

Desert Southwest. by Halka Chronic, 1986.

This is a wonderful book for anyone going to one of the parks she covers in the book. I used some of her introductory information in this handout.

5- THE CRUST OF OUR EARTH- AN ARMCHAIR TRAVELER'S GUIDE TO THE NEW GEOLOGY

by Chet Raymo, 1983.

Clear text and wonderful illustations make this book fun as well as informative. Each subject is covered on two pages, and though written for non-geologists i§'basically correct.

6- ROADSIDE GEOLOGY OF TEXAS, by Robert A Sheldon, 1979. ~

For anyone interested in Geology, this little book can inform as well as make highway travel more fun.

AUSTIN NATURE CENTER LEADERS are: Margaret Campbell and Frances Pfertner

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A Look Into Austins' Geology and Fossils

Written by N. Charbeneau, to provide background information

to the AlSD 6th Grade Rock and Fossil Field Trip

Revisions made in Spring 1984 with advise from Mary Ann Beauchemin,

Gary Gray, and Rose Farmer

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Introduction /

Geology is the study of the earth; its origins, history, and composition. Since geologists can't directly observe what the earth was like millions of years ago, they have to re-construct its history by analyzing the earths rocks and soils, observing their position in relation to other rocks, and noting the presence or absence of such things as fossils contained within those rocks. Each analysis is then pieced together to form a probably sequence of events that occurred to produce each region's geologic history.

In this unit we are going to focus on Austin's geology as it pertains to our activity site and the activities we will be doing there.

Geologic Time

The earth is thought to be at least 4~ billion years old. To deal with this vast stretch of time, geologists have divided the billions of years into various time units and named them ~ and periods. To give you a broad overview of the geologic time scale, please refer to the chart on the next page.

The first major geological event to have affected the Austin area occurred during the Pennsylvanian period (about 300 million years ago). The Ouachita (pronounced wash-i-taw) Mountains were thought to have been formed by folding and thrusting actions when the South American continent pushed up against the North American ;ontinent. See the Texas map on page 3 to find where the mountain belt was. For an explanation of these continental movements, see the theory of plate tectonics in the geologic change section. During the Triassic period (200 million years ago) the Ouachitas sank below what became the Gulf of Mexico. The Jurassic and Cretaceous periods are characterized by the sea advancing and receeding over this area depositing sediments composed of sand, clay, dead sea animals, shells and coral. These sediments formed layers which when hardened, became the sedimentary rock we find here today. Some of these layers were formed when the water was warm and shallow and are therefore softer than those layers formed when the water was colder and deeper. This produced the "step­stone effect" we sometimes see around Austin where the softer layers erode before the harder ones. At the end of the Cretaceous period, volcanic activity occurred at Pilot Knob. It can now be seen as a rounded hill (only 711 feet tall) southeast of McKinney Falls State Park. Also during this time a large mass of pre­Cambrian rock was uplifted to the west of Austin and is called the Llano Uplift (see map). This area is sometimes referred to as the central mining region of Texas and is composed of mostly metamorphic rock such as gneiss and schist, and igneous rock such as granite (see the rocks and "minerals section for an explanation of these terms).

Note on the Geologic Time Chart that while the sea was ad­lancing and retreating forming the limestone layers, various

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Geologic Time Scale

Millions Millions Charac- What of Years of Years teristic Happened

Era Ago Period Ago Life in Austin

Paleozoic 600-255 Cambrian 600-500 Trilobites, Shallow, warm sea Molluscs covers the area

Ordovician 500-425 First Limestone forming Vertebrates

Silurian 425-405 First Land Animals Spiders, Scorpions

Devonian 405-350 Primitive Fish, First Land Plants

Mississippian 350-315 First Deposits of coal Amphibians, accumulating Spore-Bearing Plants

\ Pennsylvanian 315-285 First Ouachita Mountains

Reptiles, formed, sea First retreats westward Trees n

Permian 285-230 Reptiles in Texas, Age of Dinosaurs Begins

Mesozoic 250-65 Triassic 230-180 First Ouachita Mountains Mammals sank

Jurassic 180-135 First Sea advances and Birds retreats from gulf

Cretaceous 135-65 First Volcanic activity Flowers, Llano Uplift Dinosaurs Become Extinct

Cenozoic 65-0 Tertiary 65-1 First Sea retreats to gulf Primates, Balcones Fault First (15-25 million year~ .ago) Grasses n

IQua te mary 1-0 Ice Age-Man

(Figure 1)

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BALCONES FAULT ZONE SHEl!:T I

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Physiographic map of Texas.

William H. Matthews III, Texas Fossils. An Amateur Collector's Handbook (Guidebook No. 2, Austinl Bureau of Economic Geology, 1960), Plate 9, p. 36,

(Figure 2)

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plants and animals were evolving and leaving behind their prints and bones. Fossils will be discussed in a "later section.

In the beginning of the Cenozoic era, a second major layer of sediments were deposited here when the Rocky Mountains began to erode. They sent their sediments made up of sand, rock pieces, mud, and clay by way of rivers towards central Texas. These sedi­ments eventually pushed the Texas coastline to where it is today. Because the new sediments were heavier than the previously deposited limestone sediments (made up of shells and sea animals), they com­pressed the underlying layers forcing the water out increasing the density of the limestone creating instability and stress in this region. Meanwhile, the buried Ouachita Mountains were undergoing tension and movement themselves creating the greatest stress along the Ouachita Belt (see map on page 3). Between 15 and 25 million years ago these tensions resulted in a rupture or fault along what we call the Balcones Fault Zone. The fault exposed the previously buried Cretaceous sediments so that when the cementing limestone wore away, the fossils they held were carried by water to the creeks below.

Since then two distinct geographic zones have formed in the Austin area due to the faulting and different erosion rates which depend upon the characteristics of the exposed rocks in each area. These areas are known as the:

Edwards Plateau characterized by higher elevations, a hard limestone sub-surface covered by shallow, rocky soils to the west of Austin. sometimes this area is referred to as the "Hill Country".

Blackland Prairie characterized by deep clay soils on a broad, rolling plain to the southeast of Austin.

Due to the great differences in soil and topography between the Edwards Plateau and the Blackland Prairie you can see a divi­sion in the variation of plants and animals that can be found here. Some examples are the eastern and western meadowlarks, the (wes­tern) rock squirrel and (eastern) fox squirrel, and the (western) ash juniper tree and (eastern) virginia juniper.

Rocks and Minerals

By far, the most common rock found in the Austin area is lime­stone. But what is a rock anyway? In general rocks are made up of a mixture of different minerals. Minerals are things like quartz, calcite, mica and galena. They have definite physical properties and chemical compositions. Most minerals are crystalline, that is they form crystals (pieces with flat surfaces that join at definite angles). Some minerals are also elements such as gold, iron, silver, and lead.

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Rocks are classified by the minerals they contain, how they ·~~re formed, and by their physical properties. Some physical pro­~erties commonly tested for are: hardness, luster (metallic or non-metallic), color, transparency, the color of streak it makes when drawn against a porcelain surface, how they cleave (split), how they fracture, their brittleness, and other special properties such as taste, odor, magnetism, and reaction to acids. Some of these tests you will be doing in the rock activity area.

Rocks are grouped into one of three large classes according to how they were formed. The three classes are called igneous, sedimentary, and metamorphic. As you read through the following explanations of these terms, it may help to refer to the rock cycle diagram on the following page.

Igneous rocks were once hot and fluid within the earth. They reach the surface in one of two ways. The best known way is through volcanoes. when the magma (hot molten rock) shoves its way to the surface (becoming lava), it cools and hardens quickly so that the mineral grains tend to be too small to tell apart. These are extrusive rocks and some examples are obsidian, pumice, and basalt. The other way they reach the surface is a much longer process. They cool slowly within the earth so that the minerals contained in the magma have time to form crystals. Then they are gradually exposed to the surface by uplifting and erosion. Granite is the main intrusive rock found in this area, mainly in the Llano uplift area.

Sedimentary rocks are formed through burial under layers of accumulated sediments. These sediments are composed of rock and mineral grains that have come from weathered rocks of all kinds. Rocks are weathered when water, ice, snow, wind and other agents cause them to either dissolve or break apart. Often the cementing together of these grains is done beneath the sea. Sometimes when rocks ~uch as limestone are weathered, they completely dissolve then drop out of solution and act as cement to bind othe~ sediments together. In fact, lime (calcium carbonate) along with silica (glass) and iron are the-main cementing materials in sedimentary rocks. Sandstone (cemented sand particles) and conglomerate (cemented pebbles) are formed this way along with our most common rock here, limestone (cemented micro-organisms). There are several different kinds of limestone characterized by their texture and composition. For a rock to be classified as limestone, it must contain at least 50% of a chemical called calcium carbonate (Caco3). Other common sedimentary rocks found around Austin are shale (compacted mud), halite (rock salt), and gypsum which is used in producing paint, plaster and tiles. Most sedimentary rocks are gritty and show signs of layering and many contain fossils.

Metamorphic rocks are the third class of rocks and are formed under conditions of intense heat, pressure, or both usually at considerable depths within the earth from older "parent" rocks. The minerals of the parent rock are often altered becoming more

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Rock Cycle

[Igneous, ~ crystallizatioi.

~ Sediments

organic matter heat and~ pressure

melting

~ erosion

Compaction e~sion + .-.,

lithification JS d' t I . e l.men ary .

IMetamorphicl

(Figure 3)

Pilot;s Knob as it must have appeared 100 million years ago

.... ' I j"

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(Figure 4)

From Roadside Geology of Texas by Robert A. Sheldon '.

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coarsely crystalline, harder, and tend to align in layers. You can remember the name and process by thinking of how a caterpillar changes into a butterfly by a process called metamorphosis. Some examples of metamorphic rock are gneiss (pronounced nice) that once was granite (igneous) and marble which came from limestone (sedimentary). Some other common metamorphic rocks are slate (mud), talc (baby powder!) and schist (made up of mostly mica).

All rocks exposed at the surface are gradually worn away by the actions of the weather. This weathering process can alter the appearance of a rock by softening and changing its texture. For this reason, to identify a rock, it's sometimes necessary to break it open.

Geologic Change

At the beginning of the manual we mentioned that the .geology of the earth is constantly changing. We have mentioned some types of change by discussing how rocks are formed. Other types of geologic change mentioned previously but not discussed are plate tectonics, faulting, folding, volcanism, and erosion. You will be talking about all of these processes during the course of the field trip so here is a simplified explanation of each process.

Plate tectonics is a theory that has been formulated in recent years. It maintains that the earth's crust is broken into large pieces called plates. There are two kinds of plates, oceanic and continental. Oceanic plates underlie the ocean and continental plates underlie the main land masses. The continental plates were thought to have once been joined together into a large continent called Pangaea. The plates move over the mantle (the hot, molten part of the earth's interior immediately under· the crust) by means of convection currents in molten rock. These currents are caused by warmer fluid portions rising (because they are. lighter) and colder more dense portions sinking. These movements are thought to be responsible for Pangaea breaking up. and pushing the continents to where they are today. Most geologic changes (such as faulting, fold.ing, and volcanism) occur on the edges of these plates. There are three types. of plate movements.:

1.

2 .•

Plates slipping past one another:

an example being the San Andreas Fault in California.

Plates colliding:

an example being the Alaskan Aleutian Trench

an example being the formation of the Himalayas.

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Faulting

(see drawing) Figure 6

subduction

and folding

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Crustal Plates of the World

CAROUNE PLATE I.. BISMARCK PLATE

SOLOMON PLATE . FlJl PLATE

PACIFIC PLATE

111' ..,.

EUKASlAN ~TE r n 1

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The plates are forced apart at the mid-ocean ridges by the intrusion of magma from the mant:lei this process is called seafloor spreading. The arrows show the directions of plate movement. Subduction zo~~s are indicated by small black triangles along the plate boundarie

(Figure 5)

Cross section of Plates ~ :>uthern Alaska

Aleutian Trenc Pacific Ocean

The Pacific plate is being subducted under the continental plate, creating ea=~hquakes along the zone of contact (called the Benioff zon~j. The descending Pacific plate pushes the continen­tal plate no=thward (arrow A) and downward (arrow B).

(Figure 6) n

Both figures taken from the Spring '84 issue of ·the Stanford Magazine

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3~ Plates moving apart

an example being the Baja Rift in the Gulf of California and Mid-Atlantic Rift. (As the plates move apart, new crustal material is added to each plate.

Rifts and Ridges

In all three types of movements, earthquakes and faulting are common. Volcanoes are common in the second two. There are about 8 major plates and many smaller ones in the world. Part of the North American plate boundary used to lie along the Texas coast. It now lies out in the Caribbean.

Faulting is defined as a fracture in the earth's crust accom­panied by a movement of one side relative to the other. There are many different kinds of faults named for the types of movement that occurs along them. The Balcones Fault Zone is a series of "normal faults". Normal faults occur when parts of the earth slip away from each other along along a fracture.

Normal Fault

As mentioned in the geologic time section, the Balcones Fault is thought to have occurred 15-25 million years ago and extends from Waco down to Uvalde. Most areas along the fault have dis­placements of less than 50 feet in elevation although the largest one is 600 feet. This fault is not the result of plate movement as mentioned before, but rather tensions exerted during the for­mation of the rocks in the surrounding area. Be aware that the Balcones Fault is not just one continuous fracture. It is a· series of parallel fractures along the area shown in figure 2.

The main example of volcanism in this area is pilot Knob which is located just SE of McKinney Ealls state Park. It was a small volcano active during the Cretaceous period 70 million years ago. Volcanoes form when the hot magma beneath the crust forces its way to the surface to relieve the pressure that has built up within the earth. The contributing factors that cause volcanoes to form are extremely variable as are the methods they use for extruding the magma and the volcanoes' resulting form; i.e., they don't all look or act like Mt. St. Helens. Most of the world's 600 active volcanoes are located long the plate boundaries surrounding the Pacific Ocean known as the "Ring of Fire". Nearly all of Americas I volcanoes are located along the west coast. Pilot Knob has been inactive since the dinosaurs became extinct and has been eroding ever since. This brings us

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to the last major type of geologic change, erosion.

Erosion is different from a:_ of the previously mentioned ,f") processes because it happens everywhere, continuously. It can be very slow or extremely rapid depending on the condition and struc-ture of the land and the eroding forces. If you look for them, you can see examples of erosion all around Austin. Generally the conditions that encourage rapid erosion are small soil :)article size, lack of anchoring vegetation covering the soil, steep slope of the land, and exposure to high winds and heavy rainfall. Eroding or weathering forces are mainly ice, heat and cold (freezing and thawing), snow, rain, wind, and sometimes chemical agents for example, acid rain which wears away solid rock rather quickly.

Fossils

The last major subject coverec ~n this unit is fossils. A fossil is the remains, print, or o~ ,;r indication of former plant or animal life preserved in rocks. The majority of fossils are found in marine sedimentary rocks. People who study fossils are called Paleontologists. The three requirements that determine whether an organism will be fossilized·are:

1. The organism should possess hard parts (bones, shell, teeth, or woody plant tissues). However, sometimes soft bodied organisms such as insects or jellyfish have been fossilized under very favor­able conditions.

2. The plant or ar;:. :":".3.1 must not be immediately an~ ~ta1ly destroyed after death.

3. The organism S;".. .Ld be rapidly buried in a mat~~~al that delays decomposition such as mud, fine sediments, volcanic ash, quicksand, tar, tree sap (amber) or ice.

There are many different ways that organisms can be fossilized. The method usually depends on 1) the original biochemical make-up of the plant or animal, 2) where it lived, and 3) what happened to it after it died.

Some of the basic methods of preservation ~re:

1. where the original soft or hard parts of the organism are preserved

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2. where the hard parts are altered then preserved

3. where the traces of the organism are preserved

The first type where the soft parts are preserved is rare and occurs only under very special conditions such as frozen soil ice, extreme dryness, or in tree resin (amber). Most of the hard parts preserved are parts like shells, teeth, or bones. These are fairly common types of fossils where the hard parts contain various minerals that resist weathering.

t~en the hard parts are chemically altered it's called Carbonization, Petrification, or Mineralization.

1. Carbonization is where the plant or animal decomposes slowly leaving a thin film of carbon behind that show the details of the organism. This is how coal is formed.

2. Petrification is where the hard parts are buried and infiltrated by water containing minerals which eventually replace the material that was once the shell or bone. Eventually the remains become stone as in petrified wood.

3. Mineralization is very similar but faster. It's where the hard part completely dissolves and minerals are simultaneously deposited in the void. Sometimes the originaL structure is destroyed by this process. These fossils are known .by the type of substance that replaces the structure such as calcite, silica or iron.

Fossils also consist of merely the evidence that they existed such as molds, casts, and tracks. A mold is formed exactly the way you would imagine. The plant or animal dies and falls into the sea floor. Its internal parts decay and an impression of its exterior parts is formed on the sea floor. If at some other time the mold is filled with another material and that hardens, a cast is formed. You can find molds and casts in most of the fossil bearing rocks in Texas. Tracks of an animals' movements are also found around Austin. Some of the world's more well known dinosaur tracks are located near the town of Glen Rose, Texas (just south­east of Ft. Worth). You can see a segment of them on display at the Texas Memorial Museum as well as the Museum of Natural History

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MOLDS AND CASTS

St-oe 1. A 18. crelture dies and falls to the _bed. The soft intemal Plrts quicklV decay and lie washed Iway.

mold

Stlge 2. The emplY shen is buried under accumulaling sedimenls Ind very fine _dimenl begins to 1111 the cavity.

Stage 4. Millions of years late. the hardened rock is broken open to ,eveal the cast and mold of the ahell.

(Figure 7)

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Stage 3. The ahen maleria! hal dlaolved. leaving a mold .. Sediment has filled the cavity, forming I Clst of the shell.

cast

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in New York City. Fossilized tracks, trails and even entire burrows of both invertebrates and vertebrates have been found.

~ Animals waste products are also fair game for fossilization.

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The main fossils you will find at Shoal Creek are going to b7 the Pelecypods (clams, oysters, mussels, and scallops; all b1v.alved shells), Gastropods (snails, etc.; univalved shell), and Cephalopods (ammonites) from the phylum Mollusca. You may find a few fossils from the phylum Brachiopods who also have bi-valved shells. A valve is merely a shell portion, i.e., a clam has two and snail has one. Brachiopods look much like clams except their line of symmetry dividi~g the shell into two similar halves runs through the shell while in Pelecypods, the line runs between the shells. Usually Brachiopods have one valve larger than the other. You may also find some Echinoderms who have a five fold radical symmetry like a sand dollar. See the activity section of the fossil hunt for drawings of these fossils. Don't be worried about the identification of these fossils, 95% of what the kids will find will be Exogyra, a Pelecypod.

In your fossil hunt you may want to ask them how scientists know how one fossil is older than another. Most of them have been exposed to the law of superposition which states that the oldest rocks are the deepest and the youngest ones are on the top. This will tell you the fossils' relative age but its absolute age (how old it is in years) is found by analyzing the elements in the rock surrounding that fossil. Can you figure out the relative ages of the fossils at Shoal Creek? Why or why not?

Conclusion

The study of rocks and fossils can be fun and interesting to all ages. Remember that names and dates are seldom of. importance in comparison to the experience of discovery and observation which is what the children will remember in years to come. This field trio is a motivational supplement to what.the teachers have gone over in the classroom. You are ~ot expected to teach the unit for them. However, they will be asking question about what they find and are doing and hopefullY.between this unit, the activity section, and the training, you will be able to answer most of them accurately .

. Do stress whenever possible Austin's unique geologic past. They did not get any of that in their unit and geology makes more sense when you can see actual examples of what is being talked about. Above all, have fun and think "safety first".

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Some OSS~ F ·ls You May fino ~n AUS t:~n

CRETACEOUS PELECYPODS

EXOGYRA PONDEROSA

CRETACEOUS GASTROPODS

/~~ ~J~ GYROOES

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15 EXOGYRA ARIETINA

NEITHEA

TYLOSTOMA TURRITELLA

BRACHIOPODS

d b c

KINGENA WACOENSIS

INOCERA.l\fUS

n CRETACEOUS ECHINOluS

SALENIA

/ .• ': ... -. .. .

HEMIASTER

Rock and Fossil Vocabulary List

Balcones Fault - A slip-dip fault that runs from the Waco ar,ea to south of San Antonio.

·~lackland Prairie - The rolling plains located east of Austin where soils are deep, dark and clay-rich.

Cast - A fossil reproduction of a natural object formed by infiltration of a mold of the object by waterborne minerals.

Cenozoic - The latest era of geologic time extending from the end of Mesozoic era to the present.

Cretaceous - The third and last period of the Mesozoic'era.

Drainage Basin - The area surrounding a stream bed that drains its liquid run-off into that bed.

Edwards Plateau - The "Hill Country" located west of Austin character-ized by shallow rocky soils.

Element - A substance made up of only one kind of atom.

Erosion - The wearing-away of the earth's surface.

Exogyra - A oyster-like fossil in the pelecypod class of fossils which all possess a bivalved shell and live exclusively in an aquatic environment, usually marine.

Fault - The displacement of rocks along a zone of fracture.

Fossil - The remains or traces of organisms buried by natural causes and preserved in the earth's crust.

~neous - Rocks that have solidified from lava or molten rock.

~ Marine - Something of or related to the sea. Mesozoic - The era of geologic time that precedes the Cenozoic and

follows the Paleozoic. Metamorphic - Rocks formed under conditions of intense heat, pressure

or both deep within the earth.

Mineral - A solid, homogeneous crystalline substance.

Mold - An impression made in rock by a natural object. A comple~e mold ---- would be a hollow space. Paleontologist - A person who studies life of the past as recorded by

fossil remains.

Rock - An aggregation of one or more minerals. Sediment - Material that has been deposited by settling from water or

air, usually composed of rock fragments.

Sedimentary - Rocks formed from the accumulation of sediments.

Sedimen'tation - The process of laying down and hardening of sediments to form sedimentary rocks. .

Stratification - The process of forming several horizontal layers of rock arranged one on top of the other.

=rtiary - The oldest period of the Cenozoic era.

~ Topography - The physical features of a land surface. Volcano - An opening in the earth's crust from which molten rock and

stearn issue.

c.

Key to Geologic Time Line Game

1. Llano granite (used in state capital) formed

2. Trilobites and molluscs appeared

3. First vertebrates (relatives of lampreys)

4. First land animals

5. Fish and land plants both appeared

6. Amphibians appeared

7. Reptiles and tree ferns boOth appeared

8. The age of dinosaurs began

9. Mammals appeared

10. First trees

11. Prehistoric birds appeared

12. Fi rs t flowers·

13. Pilot Knob was an active volcano

14. Austin was a shallow sea

15. Dinosaurs became extinct

16. First primates and first grasses

17. Balcones Fault

18. Ice ages began

19. Homo erectus appeared .. 20. Homo sapiens appeared

21. Ice ages ended

1,100 M yrs

• 500 M yrs

• 425 M yrs

• 405.- 350 M yrs

• 350 M yrs

• 320 M yrs

285 M yrs

• 245 M yrs

• 180 M yrs

180 - 140 M yrs

120 M yrs

78 M yrs

]00 - 65 M

65 M yrs

65 M yrs

15 M yrs

2 M yrs

2 M yrs

500,000 yrs

1~,OOO yrs

Aus tin Ns :~. re Cen ter Rocks & Fossils M Beauchemin 1/84

U Site 1.

Site 2.

Site 3.

-' ~ til Site 4.

~

Site 5.

Site 6.

1Ifj. ~''r~I:ie'':<

u Site 7.

S~.

Site 9.

Site 10.

Site 11.

Site 12.

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TWELVE FOSSIL COLLECTING LOCALITIES IN TRAVIS COUNTY, TEXAS

CHRIS CARAN, April, 1973

2·1/2 miles northw~"t of the intersection of Parkcrest and Northland Drive. on F.M. 2222. Glen Rose <A.<,~1 ~'~. limestone in roadcut (east side). Fossils~ pelecypods (clams), gastropods (snails), algae. Watch for fast M.c.-p.:-e. mov ing cars! .. . Vicinity of Highland Hills Terrace. Walnut claystone exposed in several.roadcuts m thiS are~, F08S11s~ pelecypods (clams), gastropods (snails), cephalopods (ammonites), echinoderms (sea w:chms). Ben White Blvd., one mile northwest of the intersection of South Lamar Blvd. Edwards lunestone ex­posed in roadcut (west side) on north side of Barton Creek. Fossils: pelecypods (clams), gastropods (snails). , " Red Bud Trail just west of low water bridge across the Colorado River. Edwards Lunestone 10 ro~dc':1t ~ p.. on south side of Red Bud Trail. Fossils: pelecypods (rudistids), gastropods (snails). ~ ~J1 n~ "tt:~ .... r. ""=:1. «

Pease Park. Del Rio clay and Georgetown limestone exposed in west b,ank of Shoal Cree~. FO~IIs: pelecypods (oysters) in the Del Rio clay; brachiopods (lamp shells), echmoderms (sea urchm spmes) in the Georgetown limestone. , . Ben White Blvd., 0.9 mile northwest of the intersection of South Lamar Blvd. Del RIO clay In road­cuts (east side preferable) and Georgetown limestone exposed in the south bank of Barton ~reek .. A major fault cuts between this point and site 3. Fossils: pelecypods (oyster~ .. many preser:ed m pyrate or ufool's gold"), echinoderms (sea urchin parts and spines) in the Del RIO clay; brachaopods (lamp shells), echinoderms (sea urchin spinE-.s) in the Georgetown limestone .

. M' tee' .. n I'·. "Of ) '¥trdrttrM,ar tW'· _.toldh'" 't

Intersection of South Lamar Blvd. and Barton Springs Road. Buda limestone and Del Rio clay in roadcut (southwest corner). Fossils: coelenterates (corals), gastropods (snails) in Buda limestone; pelecypods (oysters) in Del Rio clay. Watch for falling rock! Bouldin Creek bank (east side) just west of the intersection of South 5th Street and Columbus Street. Lower Austin limestone and Eagle Ford claystone in creek bank. Fossils: pelecypods (clams) in lower Austin limestone; vertebrates (fash teeth and bones), cephalopods (ammonites) in the Eagle Ford claystone. .

Northwest Park. Eagle Ford claystone exposed in banks (east side preferable) of Shoal Creek. Fossils: S.~~~~7~~ pelecypods (clams), vertebrates (fish teeth and bones) in Eagle Ford claystone. A few vertebrate ~. ~ ~ . (mammoth) bone fragments have been found in the gravels overlying the Eagle Ford claystone. Little Walnut Creek (north of Highway 290). Upper Austin limestones and claystones in west bank of Little Walnut Creek. Fossils: echinodenns (sea urchin spines, crinoid parts, and starfish) .. pelecypods (clams), cephalopods (ammonites). b+.....;, 6<..rlc.I·l'Y..~,.\. ~ , ~ '3

Yicinit! of Kirksey ~rive (south of River~ide Drive). Taylor clay exposed in several roa~cuts in this ~~t C, t/ ammediate area and Just to the west. Fossils: pelecypods (oysters), cephalopods (ammonites). Wi" LKu s~ Intersection of Manor Road and Northeast Drive. Taylor clay in hill slope on southwest corner. Fossils: pelecypods (oysters), cephalopods (ammonites). ~c:.r~~ ~ '1.&k ..

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· A Dichotomous Key to Minerals

instructions: 1. Always start with the first pairing! Don't skip steps! It may not get you to the right answer. 2. Dichotomous keys are based on two choices,; yes it has the given characteristic or no it doesn't. 3. At each pair you will be able to get to an identity or be given a number to go to next. 4. Use the simplest method to ID something first! In other words, if you can get it by color, don't try to scratch it! A bunch of scratched up specimens will not make ID easy for the next person. 5. Use black or white porcelain plates to test streaks 6. Ask counselor for help with Hydrochloric acid fizz tests

MINERAL KEY

1. a. Mineral is yellow SULFUR streaks yellow I or white; smells like rotten eggs hardness 1.5.:2.5

b. Mineral is not yellow 2

2. a. Mineral is bright green MALACHITE streaks green, HCL will fizz on it hardness 3.5-4

b. Mineral is not bright green 3

3. a. Mineral is reddish HEMATITE streaks dark reli, hardness S.5-f}./S

b Mineral is not reddish 4

4. a .. MineraI-looks metallic PYRITE streaksblack, reddish black or brqwniSf.l black, harndness 6

b Mineral does not look metallic 5 I I

5. a. Mineral is magnetic MAGN.ETITE streaks black, hardness 6

I I

b Mineral is not magnetic 6

n

n

7.

8.

U i

9.

10.

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a. Mineral is clear, colorless or white 7

b. Mineral is not as above, is gray

a. Mineral occurrs in sheets, can be scratched with a fingernail

b. Mineral is not like above

a. Mineral can be scratched with a copper penny

b. Mineral cannot be scratched with a copper penny

a. Mineral can be scratched with a pocket knife, is light purple

b. Mineral cannot be scratched with a 1 tknif poc...<e e

a. Minerai can be scratched by quartz, is pink

b. Mineral ca.nno~;be scratched by quartz, is clear

\

TALC feels soapy or greasy, can be scratched with a findernail, hardness 1

GYPSUM streaks white; can be clear, white, pink; hardness 2

8

CALcrrE streaks white; can be w bite, yellow, clear or orange; HCL fizzes on it; hardness 3

9

Flourite streaks white; hardness 4

10

QUARTZ streaks white; can come in many colors; hardness 7

TOPAZ streaks white; hardness 8

AUSTIN NATURE CENTER URCHINS, SAND-DOLLARS.e~c. FOSSIL HUNT CHAMBERED NAUTILUS.

SQUIQ, AMMONITE, etc .

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SALEHIA XI

HEMIASTEft I.

ECHINOID SPINES Xl

ECHINOID ~L4TE II

~ ~

~ ;;;st "::. ::.. :.. ~ ..

HOL.£CTY'''US ll.

HOLAST!It 1/

CRETACEOUS ECH1NOIDS

P!HTAGaflASTEIL I.

II

CRETACEOUS FOSSIL STARFISHES'

...... I. CRETACEOUS caw.s

T£XANITES I"

TU'''''LIT£S lOll

mi»1J»J1t!t IACULIT!I

lit

ACANTHOCERAS ' ..

OXYTltO~IDOC£R4S 11:" ....

p~--~!>

CRETACEOUS CEPHALOPODS

SNAILS

'''''001. III

TUWTIIJ,.A .. CIJIITM,.,.

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CLAMS AND OYSTERS (bjvaJves=2 shells-may be equal or uneQual)

P4CHYMYA . ...,

aST"!A CA"'NATA II

OSTfilU QUACNaPUCA TA x.

~HOI.ADO"TA . XI

ElCOGY"A "",£TINA x.

!X0I'tM -.-.-XI

ElCocrrM u&Y11CULA x.

,...,... ••

£I c .... TDIIIa ••

IHOCIP"III x.

GRYPHAU WASHIT AENSfS

O"Y~HAU GRAYSONANA II

II

AL£CTIltYOMA LUGU."'I II

~ ••

IILICA1U.A II

NGTD· I •

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~~ ~ ~e ~C/L J -w ~~'""V'\ W.:l ~-~ ~!» (.I, ... "\..'" ~.Jf"lA.~.:J

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7l. Guide to Identifying Rocks, l\1inerals and Fossils CJJ- VV\..'--LC.l>L ~ of. ~.~ Minerals - \.~'::)\,'\_c.~ ~~ o..r<- (,,'1'\.. ~ ~V-~ Mineral identification is based upon the following properties: '\eve...~..e...--;

.- 'VV\..~ ~ ~~"'-\ f . ~..s 1. luster - the appearance of a 111ineral under reflected light.

2. hardness - the relative ability of a Inineral to scratch another mineral or object. SOlne reference hardness incl ude a glass plate (hardness = 6), a steel nail

~J.t,...,~ (hardness ..... 5), a penny (hardness = 3.5), and your fingernail (hardness = 3). ,0 ~> 0+ 3. color - sometiInes useful, but 110t always diagnostic.

4. streak - the color of the pO'vvdery Hne left behind when a mineral is dragged across a porcelain plate.

5. cleavage - the property of a Inineral to break along certaill~ regular planes of weakness as opposed to fnlctur'e which is the property of a lnineral to break unpredictably and irregularly. . .,~

'~c.~~ 6. crystal form - the characteristic shape ofa crystal when allowed to grow freely ..w:J.L LJ-t) of.- into open space.

7. nliscellan~ous properties - ll1aglletism, smell, taste, and fizzing with Hel acid are also sometimes useful to identify nlinerals.

OU-v\.C-'" Sedimentary Rocks . ~""'-L.rcsJ"A11 sedimentary rocks fonn at the earth's surface by the activities of wind, water,

)\AcU~ chemicals, or critters. There are two nla1n groups of sedimentary rocks: U l'OcJL~

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1. clastic rocks - sedimentary roci<:s.that form by individual grains (clasts) of eroded rocks being "glued" back together by a lnineral cement· Clastic sediInentary rocks are identified by grains size and shape.

2. chemical and biochemical sedin'lentary rocks - fonn by the inorganic or biologic precipitation of minerals to fOlm the grains or crystals of a sedimentary rock. Chemical and biochelnical sedilnentary rocks are identified by the mineral conlposition.

Igneous Rocks Igneous rocks fonn froln the solidification of Inagma e~ther:

1. underground where crystals cool slowly to fonll plutonic igneous rocks with larger crystals.

or 2. abo~e ground, where the lava cools quickJy to form tiny crystals in volcanic

igneous rocks. or

. 3. both below and above ground 'vvhere the rock 'will have both large and small crystals (porphyry).

The igneous rock type name is based on:

1. crystal size - related to where and how quickly the magma solidified. and

2. mineral composition - i.e. mafic (rich in dark, iron and magnesium minerals) or felsic (rich in quartz and light-colored nlinerals).

Metamorphic Rocks Metamorphic rocks fonn underground as any buried preexisting rock (parent rock) is exposed to high temperature andlor pressure (squeezing). Metamorphic rocks are identified by:

1. texture - squeezing produces an alignn1ent of lnineral grains into sheet-like layers called foliation. The amount of foliation is related to the amount of temperature and pressure the rock is exposed.

However, not all rock types will have minerals that will become organized into layers when squeezed. These other "non-foliated" nletanl0rphic rock types are identified by:

2. color 3. mineral composition

In general, mUltiple parent rocks may produce the same metamorphic rock i.e. both a shale and granite can be transfotmed ipto a gneiss at high temperatures and pressures.

But, parent rocks with limited nlineral compositions will only become certain metamorphic rock types because the classification for these particular metamorphic rock types happens to be based upon the nlineral composition of the metamorphic rock.

For example:

quartz sandstone (having only quartz) -+ quartzite (nletarnorphic rock with only quartz)·

limestone (having only calcite) -+ n1arble (metalTIorphic rock with only calcite) . .

Sources

tables and figures are from Long, L. Geology, 9th edition.

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PROGRAM DESCRIPTION: GEOLOGY (at Shoal Creek)

Part I Basis for Program ~ Minerals, Rocks and Fossils Course Description: Float a rock, smell a mineral and find exogyra fossils

in Shoal Creek. This outdoor exploration of Austin's unique geology provides students 'with several hands on activities while testing properties of rocks and minerals.

Age Leyel: Grades 3-6 Time: 2 hours G.aat. Participants will test the properties of minerals to identify them and

their component elements, study rocks and deduce their origin, and learn how fossils form and why we have the fossils in Austin that we do.

Part II Instructional Plan Course Outline: Three 40 minute sessions:

1 st: Minerals-Discussion of what minerals are, what they are made of, and how we identify them .. "Find the mineral that. .. "­game. Discussion of answers and unique, related minerals in our collection.

2nd: Rocks-Discussion of how rocks form and what they 'are made of (their origins). "Find the rock that. .. "-game. Discuss answers and unique rocks in our collection. If time, play "Place the word in the correct category"-game.

3rd: Fossils-20 minutes: how fossils form, Austin's geologic past, what you may find in the creek, rules to follow in the creek. 20 minutes: fossil hunting and selection of a fossil to keep.

Part III Resource Support Site Needs: Three clearings near creek with minimum of ant beds and dog

poop. participant Thresholds; Up to 75 kids, 3 instructors. Transportation Needs: ANC vehicle to go to creek. Resource Needs: Fossil, minerals and rocks program boxes. Before going

to creek, make sure you have enough cardboard squares for all (25 for rocks and 25 for minerals), enough handouts for all (75 printed front and back), and enough pencils (in case their teachers didn't read our pre-pack: 50 plus extras for when points break),

PROGRAM SCRIPT: MINERALS, ROCKS AND FOSSILS

First Sessions: Minerals --- What is a mineral? The inorganic crystals or fragments of which rocks are formed. Minerals are made up of one or more elements. Use element chart to equate elements to letters, minerals to words, and rocks to sentences. How do we identify a mineral? We use traits or characteristics -- color, smell, weight, cleavage, taste, streak, hardness, luster, etc.

Explain the rules of the IIFind the mineral" game: * You may get up and move around.

* You may talk to one another and your teachers for help ... this is not a test.

* You may use the same answer on more than one; all answers are on the yellow cards.

* Please do only the IIfind the mineralll section.

* Please use porcelain for streak tests, magnets to test magnetism, and glass to test hardness. .

* Please return all minerals to the cards where they belong after you take them to the center for testing so that others will be able· to get the right answers.

Allow time for most students to finish this section of the game. Then during the last 10-15 minutes, discuss the answers; also discuss unique and related minerals in our collection (large quartz crystal, examples of pyrite, book of mica, copper, malachite, silver hematite).

Second Session: Rocks --- What are the three kinds of rock? Igneous, sedimentary and metamorphic. The rocks are divided into these three types based on how they form.

Igneous rocks come from magma within the core of the earth. It arises. through volcanoes or cracks in the earth IS surface caused by earthquakes. Intrusive igneous rocks cool inside and are spewed out as a solid (often cooled' very slowly). Extrusive igneous rocks pour our of the volcano as a.liquid, then cool once they are outside (often they cool very quickly). What are some examples of igneous rocks? Granite. Does it cool quickly or slowly? Slow, leaving lots of time for crystal development. Do you think this is an intrusive or an extrusive? Int~sive, it cools slowly because it is inside near the heat source. Another example? Obsidian. Do you think it slow or·fast? Very fast, has no time for crystal development. Is it intrusive or extrusive? Extrusive, it is able to cool quickly because it is far away from the heat source.

Sedimentary rocks are formed by sediments which' are carried by wind or water and deposited in layers or strata. Do you know what it is called when wind or water carries sediments? Erosion. And when the wind or water stops moving, the sediments being carried are dropped or deposited in layers. What are some examples of sedimentary rocks? Sandstone, and the sediments n that make it are mostly sand. Limestone, made of silt and sand and crushed shells. Conglomerate, made up of m~ny kinds of sediments (may include ciay., sand, silt, pebbles, plant bits, minerals, shell$, fossils, etc. usually not layered).

u GEO- script continued

Metamorphic rocks are rocks that have changed form. They used to be either igneous or sedimentary. Heat and pressure cause this change --- heat comes from the core of the earth and rises, pressure comes from gravity pulling the things on the surface of the earth down toward the center. The rocks in the middle layers feel both the heat and the pressure and these are the ones to change. Examples of metamorphic rocks? Marble which used to be limestone, gneiss which used to be granite, slate or schist-which starts as shale and goes to shale then schist.

Explain the rules of the IIFindOthe rock" game: Rules are the same as in mineral game except that the only test material in the center is water for floating.

Allow time for game, then go over answers in last 10-15 minutes; discuss the unique/related samples (limestone color variation, gneiss and Llanite, basalt, polished marble, geodes). If there is extra time, use word cards from other game to review concepts.

Third Session: Fossils -- See Fossil Hunters program script.

For more detailed info see attached: A Look Into Austin's Geology and Fossils.

/" . ,- ---

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Guide to Identifying Rocks, Minerals and Fossils

Minerals Mineral identification is based upon the following properties:

1. luster - the appearance of a nlineral under reflected light. 2. hardness - the relative ability of a mineral to scratch another mineral or object.

Some reference hardness include a glass plate (hardness = 6), a steel nail (hardness -.. 5), a penny (hardness = 3.5), and your fingernail (hardness = 3).

3. color - sometimes useful, but not always diagnostic. 4. streak - the color of the powdery line left behind when a mineral is dragged

across a porcelain plate. s. cleavage - the property of a mineral to break along certain, regular planes of

weakness as opposed to fracture which is the property of a mineral to break unpredictably and irregularly.

6. crystal form - the characteristic shape of a crystal when allowed to grow freely into open space.

7. miscellaneous properties - nlagnetism, smell, taste, and fizzing with HCI acid are also sometinles useful to identify minerals.

Sedimentary Rocks All sedimentary rocks fonn at the earth's surface by the activities of wind, water, chemicals, or critters. There are two main groups of sedimentary rocks:

1. clastic rocks - sedimentary rocks that form by individual grains (clasts) of eroded rocks being "glued" back together by a lnineral cement. Clastic sedimentary rocks are identified by grains size and shape.

2. chemical and biochemical sedimentary rocks - form by the inorganic or biologic precipitation of minerals to form the grains or crystals of a sedimentary rock. Chemical and biochemical seditnentary rocks are identified by the mineral composition.

Igneous Rocks Igneous rocks form frolll the solidification of tnagma either:

1. underground where crystals cool slowly to form plutonic igneous rocks with larger crystals.

or 2. above ground, where the lava cools quickly to form tiny crystals in volcanic

igneous rocks. or

3. both below and above ground where the rock will have both large and small crystals (porphyry).

The igneous rock type name is based on:

1. crystal size - related to where and how quickly the magma solidified. and

2. mineral composition - i.e. mafic (rich in dark, iron and magnesium minerals) or felsic (rich in quartz and light-colored minerals).

Metamorphic Rocks Metamorphic rocks fonn underground as any buried preexisting rock (parent rock) is exposed to high temperature and/or pressure (squeezing). Metamorphic rocks are identified by:

1. texture - squeezing produces an alignment of mineral grains into sheet-like layers called foliation. The amount of foliation is related to the amount of temperature and pressure the rock is exposed.

However, not all rock types will have minerals that will become organized into layers when squeezed. These other "non-foliated" nletamorphic rock types are identified by:

2. color 3. mineral composition

In general, multiple parent rocks may produce the same metamorphic rock i.e. both a shale and granite can be transformed into a gneiss at high temperatures and pressures.

But, parent rocks with limited mineral compositions will only become certain metamorphic rock types because the classification for these partiCUlar metamorphic rock types happens to be based upon the mineral composition of the metamorphic rock.

For example:

quartz sandstone (having only quartz) -+ quartzite (metamorphic rock with only quartz)

limestone (having only calcite) -. marble (metamorphic rock with only calcite)

Sources

tables and figures are from Long, L. Geology, 9th edition.

.... 'hat .. ,- ~--

168 • GEOLOGY

u Metamorphic Rock Classification

Color Rock name Distinctive features

Marble Reacts with hydrochloric acid (HCI). Color streaks or blotches may be present. Look for

"- calcite rhombohedrons if coarse. Rare "ghost 0 "0 u fossils." l: .:.0

Quartzite Interlocking quartz grains fracture across original grain boundaries. May have a sugary

"'0 texture; smoother and harder than sandstone. ~ -.s .:s c Serpen~inite Lime green to dark green or black; dense. • Q) = ~ Slickensided surfaces (striated by internal Q Z eo

movement) are common .

.:..:: u Hornfels Dense, fine-grained rock with conchoidal ~

:0 fracture. 9 >. E Anthracite Shiny, low-density black rock; may have eo

.:..:: coal semi-conchoidal fracture and display partings "-~ or banding. "0

Crystal Rock name Distinctive features

u size

u Slate Dull to shiny; splits into thin slabs. Harder 'a v.: 0- than shale. Commonly dark gray, brown, red, u ~

~~ or green . "- C .~ u

. .. .'

t. :0',

. . '

E Phyllite Nearly invisible mica crystals impart satiny

sheen on foliation surfaces. Commonly gray

"'0 or gray-green.

~ -.s Schist Visible aligned platy or elongate minerals C5 ~ impart a foliation. Mica abundant; garnet or

staurolite crystals common.

Amphibolite Dark, dense, mafic rock with aligned horn-blende crystals.

:r. f1l:= e!l-:r. Gneiss Coarse-grained rock with alternating light ..EC

u (felsic) and dark (mafic) layers due to segregation of mineral species.

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Typical parent rock

Limestone, Dolomite

Quartz sandstone

Mafic or ultramafic rock

Any fine-grained rock

Lignite, bituminous coal

Typical parent rock

Shale, siltstone. silicic volcanic rock

Shale. siltstone

Shale, phyllite. volcanic rock

Mafic igneous rock. graywacke

Any silicate rock

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I t _f _

METAMORPHIC ROCKS • 167

Increasing degree of deformation

quartz sandstone

original rocks

Micas appear. Clay minerals disappear.

Garnet and staurolite appear. Amphibole

~~~~~~~~~~~

low medium

metamorphic grade

Figure 10-1. Progressive Metamorphism of Different Parent Rocks

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Definitions

Bardness

Austin Nature and Science Center Rock and )lilleral Guide

compiled by Katberine Stewart 11/01

Wben tbe mtneral collector speakS of the bardness of a Dllneral, !Ie always means t!Ie scratch bardness. ThIs IS tbe resIStance wMcb a lIlIneral exMblts w!Ien it is scratcbed WIt!I a s!Iarp­edqedroatertal. The concept of scratch hardness was Introduced more than 150 years aqo by the VIennese lIlIneraloqtst Frtedrlch Mobs (l17B-18B9). USlnq ten lJllnerals of d1ffertnq bardness, be drew up a comparattve scale (Mob's Scale of Bardness), wblcb IS valt<l tbrouqbout tbe wbole world to tbe present day. NlIlUber 1 IS tbe softest cateqory, 10 tbe hardest. The ll1lnerals Wltb t!Ie IntermedIate values scratch tlie Dllneral deslqnated Wltli lesser bardness and are scratc!Ied by the lJ1Ineral WIth the next hardness on the scale. Minerals of equal hardness do not scratcb one another .

. .,. U Streak ....

u

The streak color, also called t!Ie powder color or streak for sbott, Is an objecttve means of deterll1lnlnq lIllnerals. The streak color always reproduces tlie same llnlqlle, constant color intrinSIc to tDe whole lJ1tneral. With fluorHe, for exaro.ple, the streak color IS always whHe, reqardless of whetlier the flllorHe looks yellow, bIlle, qreen or black. In order to obtain tlie streak color, a corner of t!Ie spect1Uen IS rubbed on a small, unqlazed porcelain plate, tbe streak plate.

Luster

Many ll1lnerals bave a charactertstIc luster. It ortqtnates from the llqnt reflected at the surface of tne stone and IS dependent on tne refracttve Index of a ll1lneral and tne ll11neral's surface cnaractertsttcs, but not on tne color.

Cleavaqe

Qeavaqe IS tlie spltHlnq of a lJllneral alonq smootb surfaces or planes. Wbetber a Inlneral can be cleaved or not dependS on tne lattIce stracture of tne crystal.

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u Mineral

A mIneral IS an entIty wnIcn occurs naturally as part of tne Eartb's ernst or tbe Moon's surface. Most ln1nerals nave a specIfic crystal form. The scIence of ln1nerals Is called ln1neralogy .

Rock

A rock IS a natural llltxture of ln1nerals. It forms an IndtVtdual qeoloqIcal body of consIderable extent. The sctence of rocks Is called petrology or petrograpny.

Iqneolls Rocks (1I1aq1l1atites)

Develop wben llq1Ild molten rock.maqIn~ solldifIes In tbe Eartn's ernst or on tbe Eartb's surface.

Sed1l11entary Rocks (SedllIlennteS)

Develop at tbe Eartb's surface froIn tne weatnertnq products of otner rocks.

U Metafuorpbic Rocks (1I1etaJllorpbites)

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Develop tbrouqb tne transformatIon of otber rocks In tne Earln's ernst as a reslIlt of qreat pressures and blqb temperatures.

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)Itneral Bardness streak Lllster Oeavaqe

Asbestos 2 whIte vItreous perfect CalcIte 3 white vItreous perfect Galena 2.5-3 qrey-blk metallic perfect Gypsum 1.5-2 white pearly perfect HematIte 6-6.5 red metalllc none ~aqnet1te 5.5 black metalllc 1lIlperfect

~Ica 2.5-3 whIte pearly perfect U PyrIte 6-6.5 drk.qreen metallic 1lIlperfect

Quartz 7 colorless vItreous none Sulphur 2 whIte qreasy none

Talc 1 whIte qreasy perfect

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Minerals

Asbestos---It IS tbe COl11lllon name for a group of naturally-oCCUITlng slllcate ll1lnerals nat separate Into tbln, but strong flbers. There are SIx asbestos minerals which have been used commerClally-cIrrysotlle, amosHe, crocldolHe, antbophylllte, tremollte, and actlnollte. Asbestos IS not combustible, bas blgh tenslle strenqtb, bas good tbermal and electrtcal Insulating properttes, Is moderately resIstant to cbelJllcals, and bas good friCtional properties. It Is durable, flexible, strong and resIstant to wear. Thus, asbestos bas been used for tbousands of cOl11lllerClal and public appllcatlons Including: Rooflnq and flOOring Products, Textlles ... etc. 110re recently, asbestos dust bas been recoqnlZed as being cancer-lnduClng.

CaIcHe---Usually translucent wnHe, but sometllnes yellow, brown, gray, blue, pink, or green. Its lJ1Ineral name Is calCl1[1Jl carbonate and H Is one of tbe most abundant lIlinerals In Texas. CalCIte fOrIllS a vartety of crystal sbapes, but always wHb cleavage In tbree directions tbat are not at rIgbt angles. Used In tbe butldtnq Industry, as raw matertalln tne cIte:tnlcal, qlass and cellulose Industry, and In tIte smeltlnq of Iron ores. Iceland spar IS a clear, colorless, rbombobedral vartety of calcHe wHb marked double-refraction. Used In optical Instruments.

GaIena---It IS the heavy, metalltc lJlInerallead slllfHe. Some speCl1J1ens break Into perfect cubes when struck. Jl1Jlost always Intergrown wHh spbalerIte. occurs In vems, stocks, and layers. )]e )JJ.ost l1J1portant lead ore.

G},])SllDl---It IS a colorless, soft 1J1lneral wblcb occurs In salt deposHs, and In ore 1J1lneral deposHs. It S01JJ.etl1J1es occurs In rounded sbapes called Rosettes or Desert Roses wblch look me flowers. GypS1[1Jl that IS transparent In blocks of tIttn crystalltne sbeets Is called selenite. It forms In cracks and spaces between rocks, espectally clay sedllllents. Used as blltldtng materials and raw materIal In the cerarotc industry.

BematHe---RematHe, ("'bema" Is latin for 'led"), sometl:tnes looks silver, but leaves a red streak. It Is tbe most abundant and l1J1portant ore of Iron. It Is often found as a cementlnq aqent in sandstone.

M:aqnetHe---It IS mainly known for Hs magnetism, black color, and bardness. It is an l1J1portant tron ore In tbe manufacture of steel.

Mica---Group of slllcate llllneraIs composed of varylnq amounts of alumln1[1Jl, potaSSl1[1Jl, lllagneSi1[1Jl, Iron, and water. llllJllcas form flat, plate-me crystals. crystals cleave Into smootb flakes. BiotHe IS dark, black or brown lIlica; lIluscovHe Is lIgbt-colored or clear mica.

Pyrtte---Reflects a pale, brass yellow. The most c01l1lJ10n forms are cubes wHb faces strIated. It Is known as "fool's gold". It Is dlStinglIlsbed from gold by Hs bardness. Its cblef use IS a

U source of sulfur for sulfurIc acid.

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Qllartz---The name quartz come from German ll1Iners' lanquaqe of the }llddle lqes. one of the most COlJ1lJ1on llllnerals. The colortnq Is amazinqly variable because It may be whtte, gray" red, purple, pink, yellow, green, brown, and black" as well as belnq colorless. It is sillcon dioxide, bas a bard qlassy surface, and occurs In many sbapes sucb as clusters, slnqle pOInts, or solld masses. Quartz Is found In all threecateqortes of rocks. It Is tbe raw material for the qlass and ceramIc Industries. Used WIdely as qemstones and ornaments: ametbyst, rose quartz, smokY quartz, tlqer's eye, aventurtne, cttrlne, etc.

Slllpltllr---}lay be yellow or brownish wtth a greenish tlnqe. lias a unIque odor. It mainly occurs at or near the I1lns of actIVe or extinct volcanoes. Sulphur Is the raw material for the production of sulphurtc aCId and Is an I1J1portant basIc material for the manufacture of InsectiCIdes. It IS usually lJlIned by melttnq it underground WIth superheated steam and pUlllptnq the llquld to the surface where It cools and hardens.

Talc---}lay be colorless, wblte, greenIsh, or yelloWIsh. Feels greasy. Used for llqht-fast colors, finely ground (known as talCUlll) as base for oIntments and powder, for hlqh-voltaqe Insulation, and for fire-resIstant construction materials. Talc that Is massIVe and compacted Is known as soapstone.

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Rocks

Iqneolls

Basalt--- Colors may ranqe from grey to blact and also brownlsD. Older varieties are greenlsIt or browntsIt red. The texture of basalt Is usually fine gratned to dense, only very occasIonally coarse qratned or qlassy. Basalt Is tIte most WIdely distributed of all volcanic rocks. Basalt Itas many varied uses as a natural stone because of Its good qualHtes and Its WIde dlstrtb1Itlon. }lelted basalt Is a raw matertalused In tIte production of 1Iltneral wool as well as tIte base material for ltlqItly resistant floorInq slabs and ltnlnqs.

Grantte---The name granite derIVes from tbe latin ('"qranum" = grain). Granite varies In Its color fromltqbt to dark. Its major lIlInerals are quartz, feldspar, and lIlIca, wlllcIt create a coarse-grained texture. Granite IS wIdely lIsed stone for b1l1ldlnqs and decorattve work. It wears extremely well and Is ItlqItly resistant to weatIterlnq becallse of Hs blqb qlIartz content. Grey varieties are used for cobble-stones, kerb-stones, etc. Colored qranHes are used as raw materIal for sClIlpture and, wIten cut and poltsIted, as claddlnq for bulldlnq, for floor coverlnqs and s11Il1lar slIrfaces.

Uantte---A type of Texas plllk granite found nowItere else In tbe world. LIanne's lInlqueness reslIlts:from crystals of Sky-bllIe qlIartz lJltnqled wttb tbe qranlte's ruSty-Pink feldspar and otIter nilnerals. The rock IS lInlIsually bard, and was quarrIed at one tllJle for blIndlnq stone. The qlIartz IS bllIe becallse of CDrolIlllIlU 1lJJ.plIrttles .

. Obstdtan---It IS a compact natural qlass. Named after tIte Roman ObsllIS wbo In anCIent tlllles fIrSt brouqItt a piece of obSIdian from Etltlopla to Rome. It Is a stltca-rlcIt volcanic rock. The color IS dark, qrey, brown to deep-black and bas a qlassy texture. 0 bsldlan IS volcaniC, formed by tile very rapid cooltnq of VIscous aCId lava. In tIte Stone Aqe obsidian, toqetIter wttll fltnt, was a blqItly valued raw material for utensils and weapons on account of Its sItarp edqed fractue and Its great bardness.

PlIMce---P1l1IlIce (latin: "foam") IS a frotIty volcanic rock. Its color IS lISlIally llqbt grey to yellowtsb, rarely red or In dark tones. P1I11llce Is sl1nllar to a batll sponqe becallse It IS riddled WHb pores of trreqular or oval sbape wItlcb are lISUally not connected WHIt one anotIter. Because of tltls Itlqll pore vollIlUe, wllicb can reacIl85%, plI1Jllce floats on water. pu1lltce IS formed wben lava spews out of tIte volcano and cools very qlIlckly. Plumce IS used In tIte productton of llqlltwelqItt blIlldlnq stones. The advantaqe of tltese lles In tItelr ltqIttwetqbt and In tbe qoon Iteat InSlIlatlon tIter proVIde. The lIse of plI1J1lce as a qrtndlnq materIal In tecItnology, and for cosmetIc plIrposes, IS due to tIte fact tbat H Ilas no sbarp-edqed crystals wDtcD cOlIld bave a damaqlnq effect, and tItat tile rock slIrface always rematns rouqIt and Itas a qoon qrtp.

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Gneiss---The name qnelss Is from tbe lanq1laqe of German miners In the Erzqeblrqe. GneIss bas l1qbt or dark colored bands as well as a coarse-qratned texture. Sandstone or qranHe can become qnelss under beat and pressure. The most common mInerals found In qnelss are quartz, potaSSlllln feldspar, and sodium feldspar. Used as bulldlnq stone, aqqreqates, CItlpplnqs, thIn spliHinq types for claddlnq, and earlier used as rooflnq mes.

narble---The term "marble", Is Greek for "SItlnllnerlnq block of stone". }lade of calcIum carbonate. }larble forms from llmestone by metalIlorpblc recrystalllzatlon. }lay be a WIde ranqe of colors. It Is wbHe wben pure calcHe or dolomtte, but often contains lJnpurttles tbat color H or g1Ve It streaks. It bas a medium to coarse texture. Marble IS used In claddtnq, interior arcbltectare, table tops, ornaments, and control panels. Takes a pollsb well, but very quickly becomes dull In tIte aIr.

Scbtst---The final product of tIte alteration by beat and pressure alone of a mture of bydrated and oxIdIZed mInerals. TIle factors COlnlllon to scblsts are a fine to medlum-qratned texture, very distinct scblstosIty, and a feldspar content of less than 20%. Scblstoslty IS tbe distinct parallel texture wItlcIt IS rerotnlscent of sedllnentary beddlnq. There are a qreat many types of scItlst. The rocks are destqnated accordtnq to outstandInq properties sucb as notable minerals or color. Scblst IS stronqly fol1ated and can easlly split Into tbln flakes and slabs.

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SedimeJltary

Cbalk---Cbalk, (wrtttnq cl1alk), IS a l1qbt colored llInestone. It Is usually snow-wl11te, occasIonally l1qbt qrey or yellowtsl1, and porous. Cltalk bas a flne-qraIned texture and It forms from tbe bard parts of mtcro-orqanlsms, especIally alqae and foramtntfertds. JlInost pure calcHe-aqqreqate.

Cbert---Its appearance ranqes between qrey, yellow, brown, and reddisb. It is massIVe and bard lIlicrocrystalllne quartz wttb a flne-qraIned texture. It forms by tbe accumulatIon of stllca, posSIbly In a colloIdal form on seabeds. H IS a bard rock tbat cannot be scratcbed WltI1 a knIfe. It fractures Into sbarp, useful edqes. Derefore, It was used by NatIYe Amertcans to make tools.

conqlolllerate---Conqlomerate, (latIn "rolled toqetber"), IS a consolIdated qravel composed of rounded water-worn pebbles. Grey, blmsb, and yellow colors predolIlinate. They are reddIsb wbere tbe cementlnq aqent Is stronqly tron-rtcl1. It bas an uneven, qranular, coarse­qralned texture. The parttcles may vary larqely In sIZe Wltbln anyone sample. ThIs variety of sIZe IS called poor sortlnq wbere tbe rock may consISt of rocks as larqe as boulders as well as pieces as small as a slnqle pea. Conqlomerates usually bave larqe opentnqs between tDe qravel partIcles wbtcb Is filled by some qround mass sucb as sand or mud. ThIs disttnqrrisbes It between stl11ilar artifiCial stones. Solid types are used as blIildinq stones and for monlUIlents. Less co.~sOl1~ated conqlomerates are used for gravels and cblpptnqs.

Ltlllestone---It IS tbe most abundant sedtlJlentary rock. It IS composed of calctlIl11 carbonate In a finely qranular texture. The mineral calCite (calCilIl11 carbonate), can make up to 95%. Its color varies dependlnq on wbat constItutes fie ll1nestone. LI1J1estone is made in tIte sea from fraql11ents of tbe bard parts of anllnals and plants, from pbystcal preCipItation of calcareous mud, and from calcareous prectpItatlon by orqanisms. The orqantsms blIlld up tbetr support structures from calctlIl11 carbonate wblcb bas been dIs·solved In tbe water, and tbese structures accumulate after deatb on tbe sea floor. They remain eHner as complete unHs, as broken skeletal remaIns, or finely broken up as calcareous mUd. Used In tbe blIlldInq Industry for cement production, blItldinq stone, In tbe manufacture of suqar, for tbe manufacture of qlass and paints, as addttlVe In tbe smeltlnq of iron-ore, and also as ferttliZer.

Karst---It Is a l1qbt colored rock wttb a fine-grained texture. It forms a dtsttnctlYe landscape (topoqrapby) tbat can develop wbere tie underlytnq bedrock, often llInestone or marble, Is partIally dissolved by surface or qrolInd water. It IS cbaractertzed by slnklloles, caves, and underqround dramaqe.

Sandstone---Rallqes In color from pure wbIte to solid black. Formed of sand cemented by stllca or iron oxIdes, some types are soft and easny abraded; otbers are vtrtually llnpervtous to weatbertnq, even touqber tban qranIteI lias a flne-qralned texture. sandstone IS always layered and found wbere anCIent seas used to exist. It was used as butldtnq stone In earlIer tllnes for catbedrals, castles, and presttqe butldlnCJs.

Mineral Information

V Three classes of useful minerals: metals, non-metallic products, and fuels.

Metals

Iron Aluminum Silver

Mercury Copper Zinc

Non-metallic products

Building materials Gypsum Nitrates Abrasives Phosphates Potash Limestone Sand Borax Talc Quartz

Fuels

Coal Petroleum

House Construction

Ore Hematite Limonite Magnetite Azurite Malachit~. Chalcocite Galena Sphalerite Cinnabar Bauxite Quartz Kemite Borax Limestone

Metal Iron

Copper

Lead Zinc Mercury Aluminum Silicon Boron

Calcium

Use

Uranium Platinum Gold

Tin Lead Magnesium

Precious and semi-precious stones Turquoise Topaz Gamet Tourmaline Diamond Zircon Sapphire Ruby

Natural Gas Atomic (Uranium)

Beams, girders, posts, nails, machines, screws

Electric wiring, gutters, roofing, pipes

Pipes, paint, caulking Galvanizing pipe, sheet metal Electric switches, thermostats Siding, windows, doors, roofs Glass Glass

Cement, building stone

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ftndthe MINERALthaL

1. looks'like gold

2. has needle Dke aystals

3. looks WOOlly or hairy (do not open)

4. is thin and flaky

5. is yellow and smeDs

6. looks like silver and is heavy

7. is magnetic

8. feels smooth like soap

9. Jeaves a red streak on porcelain

10. is shaped tike a slanted cube til

11. is co1ortess and SO soft that you can saatch it with your ftngemai1

12..is colorless and so hard that you can ~tch a piece of glass with it

13. is colorless and is too hard to scratch With your fingernail, and

too soft to saatch the glass

Pyrite--fools goIdll- jron and sulfur

Quartz- purple- amethyst. pink-is rose q.uartz

Asbestos- _ insulation (doesDl cgnduct beat) bad for lunp

Mica-used in MoSCOW before glass­used in oven windows Cdoesn1t conduct heat)

SuIfur- makes "mtton ea smell-. used on matches. in other minerals combined with elements like iron andJead

GaJena- lead and sulfur Jead ore

Masnetite- iron ore. only stmn&Jy malDeHc mineral

Talc- very soft, used to make talcum powder

Hematite- =tlema· means red. hematite sometimes looJcs sDver but leaVes a red streak

Calcite- rhombohedral shape due to cleva.- main mineral in limestone

~- sedimentalY mineral fonned W evaporation of sea water­bardness of 2

Quartz- hardness of 7. glass 5.5

ftndtbeROCK.tbaL

14. is a common sedtmentaty rock in Austin

is. looks Uke wood

16. could write like chalk

17. is Ught and floats in water

IS.looks like black glass

19. was used by Indians to make tools

20. was used to build the Texas state capitol

21. is layered With shiny mica flakes in it

22. is a white matamOtphtc roclc that once was timestone

17' Which rock or mineral is your fayorite?

limestone can be white. amy. tan. arbJackl can be crumtW. saUd I can red~ed as in cave fonnationsl used as building stone and to make cement

Petrified woOd - minerals fl)Jed the spaces and turned it to rock

cbalk- made of sheDs of miqoscopic ore'" organisms Oimestone)

Pumice- bas traA*' air! used as buildtna material! to stone wasb JI,ani

Obsidian- looks clear in thin sHees I Was prtsed by Indians for making moJ&

Cled! mtqoscopcqystalsof quartz. fonn in Umestone I common rock of river terraces

Granite from the llano area- pinlc. qystaIs ofortboclase

Scbtst- found in the qeek near Enchanted Rock

White marble

_-~~OG'1RA (oyster)

__ GRYPHA!A (oyster)

__ PElECfPOO (clam)

GASTROPOO (snan)

__ .... ECHIt-l)IO (\rChtn)

___ CEPHALOPOD (ammcntte) ,

__ .... ' lME STOtE , '.

_____ SEDIr-£HT ARt ROO< WITH LAYERS ___ OUAATZ

U O£RT

__ .... CALCITE

__ JRON COt,GETIc:..

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tiE··· . . . . .. . ... . .. .. .

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_~FOSSIL ~SS!CH ~ rna .

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combined, the result is a rock. I pass around large pieces of different kinds of granite, showing the students how to recognize the minerals quartz, feldspar, and mica in the rocks. Typically, students ask such questions as, "Why are the minerals all different?" (chemical compo­sition and atomic structure), "Can I build a rock?" (Yes, but only a model, not the "real thing!"), UWhat is that mineral or rock used for?" (it depends on the sample being looked at), and UWhy is one mineral kind of square and another is flat?" (atomic structure).

The National Science Education Standards state that students in grades K-4 have an understanding of the properties of Earth materials, including the physical properties of those materials. By grades 5-8, study includes the geosphere, with emphasis on changes in the Earth's crust as shown by the rock cycle. By grades 9-12 most students feel they are utoo old" for these activities, but standards to be learned at this level include the structure of matter, to which these exercises can readily be applied.

Samples for Students Imagine students' reactions when they enter the class­room prepared to study minerals and rocks, only to discover toys-different colored blocks-at each desk! The first question asked, with wide eyes and huge smiles, is often, uCan we build something?" Strange as it may seem, this is an effective way for students to begin exploring the characteristics and relationships of min­erals and rocks. Few students are able to resist these simple materials, and the teacher is able to guide their learning without having the unbendable rules and writ­ten exercises that "tum off" so many students.

For nearly 20 years, I have conducted hands-on activities where students build crystal models from plastic building blocks. This model-building activity demonstrates Piaget's idea of concrete level of think­ing without being technical. Piaget believed that chil­dren, especially ages 7-12, needed concrete objects to understand and reinforce learning (e.g., the differ­ences between minerals and rocks).

To begin the activity, I show students samples and color photographs of common minerals and indicate that minerals are the basic geologic materials that make up the solid part of our planet. It is worthwhile for teachers to invest in display quality samples of a few common minerals such as those listed in the table at right. You might check with local geologists or rock and mineral clubs whose members are often willing to donate samples to your classes or share collecting localities. Depending on your geographic location, there may be mineral and rock stores that sell speci­mens. I find such places to be excellent sources of

ALL ROCK IMAGES ARE THE PROPERlY OF AMETHYST GALLERIES, INC HTTP://MINERALGALLERJES.COM!

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Table 1. ' ..' . ~£J,.,(tr;;}.~2.. ~i;:J k\~l~ ~:.';:~';t: _;~;: i- .<);l~<':::'~·:~~. ,'OJ: :.F;,

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based on an idea by Anita Gustafson

Who would want to eat a rock? Not you, I hope. After all, if you chew on a

rock, you'll crack your teeth. Who wants that? And swallowing rocks whole doesn't make much Sl'11Sl' eitller. A tillY rock would probably just go down into your stomach, take up some ham­burger room for a while, then pass right through your body. And you'd choke on a bigger rock

Some animals, however, do eat rocks. It's an odd practice, but it's been going on for ages.

PLESIOSAURS Probably the first rock-eating animals swam

in shallow bays near shores covered with strange, cone-bearing trees. These creatures, called plesiosaurs (PLEE-zee-uh-sawrs), disap­peared along with the dinosaurs. But some cI<)se cousins of the plesiosaurs- the crocodiles- still swallow rocks.

Why? Scientists aren't sure. But many of them think the plesiosaurs of long ago ate rocks for the same reasons crocodiles eat the~ today.

CROCODILES When a hungry crocodile spots an antelope

on a riverbank, the crocodile swims quietly toward its prey. It stops in front of the ante­lope and waits for the creature to lower its head for a drink of water.

While it waits, the crocodile lies very still wit h only its nose and eyes above water. It can do this probably because of the rocks in its stomach. They help to keep the top-heavy and tail-heavy animal from turning over.

Suddenly the crocodile pushes its head out of t he water, opens its powerful jaws. and snaps then1 shut around the surprised antelope's

-n e ¥ 51,.

head. Then the crocodile drags the struggling antelope underwater. The weight of the rocks in the crocodile's stomach helps the animal dive to the bottom of the river and hold the ante­lope there until it drowns.

Later the crocodile tears off a chunk of meat and gulps it down. The food goes down to the crocodile's stomach. There strong muscles chum the food and the stomach rocks together. The rocks probably help to grind up the food so the crocodiles can digest it better.

PENGUINS What do penguins have in common with

crocodiles? They eat rocks too. Scientists once removed ten pounds of small stones from the stomach of one "greedy" penguin!

But why do penguins eat tiny rocks? No one knows for surc. It's possible the rocks help di­gest food. But the penguins usually eat soft food that's easy to digest anyway.

Penguins are good swimmers and divers. They have to be. They catch all of their food in the water. Some scientists think that the weight of the stones makes swimming and diving easier for the birds.

When penguins molt, or lose their feathers, they cannot go into the water. They have to stay on land. One scientist suggested that the penguins may eat rocks at this time because they are bored and have nothing better to do.

ROCKS ON TIlE MENU So, if you ever go out to dinner with a croco­

dile or a penguin, be prepared! One of the creatures may want to eat you. The other may order rock stew. The End

15

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Specimen:

Locality: Ma~ification:

Specimen Grade: CoUection: Photograph:

MAGNETITE Var. Lodestone

Lodestone (magnetic variety of Magnetite) with nails and and Magnetite fragments attached to it

Iron Springs, Iron Co., Utah +1

A

Hershel Friedman

Hershel Friedman

l"t~netite Im~ges

• B~~klQJb.~ roi.nel"ruJv1&g!l~liJe • a~~k to ~h~Jll1_a.g~_Q~t~IY._:~M.~gl1~tit~ • Back to the Im8:ge Gallery-=.L..9_d~stQne • Im~_ .. fil~JJ~.lp.

HOM! MINElALS A-l GEMS1'QNES RESOURCes GLOSSARY !MAlt US

C.9P'yrigbt © 1997 - 2000 Hershel Friedman, all rights reserved.

MAGNETITE t

ffiagll..:ttr .. · • IlllnerJI 72.2.;

The Mineral and Gemstone Kingdom Help Pictures ..

" Chemical Formula Fe2+Fe3+ 0 2 4

" Composition Iron oxide. May contain many impurj.t.i.e$ partially replacing both the first and the second iron.

" Variable Formula (Fe,Mn,Mg,Zn,ND2+ (Fe,AI,Cr,Mn,y)3+ 204

• Color Black

• Streak Black

• Hardness 5~-6~ ,. Crystal Forms (Isometric) Crystals are usually well-shaped 9_qt~be~drol1s, and less commonly goqecanedrons. and Aggregates They may also be an interesting combination of the two. Seldom occurs in cubic crystals.

Crystals are usually striated, and some octahedral crystals contain layer growths. Also occurs rn§$$ive, griJiD~, in veins, as large embedded gr~in~, and as rounded crystals.

• Transparency Opaque

II Specific Gravity 4.9 - 5.2

~ Luster Metallic

" Cleavage None. May exhibit p~rting.

" Fracture Subconchoidal to uneven

• Tenacity Brittle

" Other 10 Marks Strongly attracted to m~gn~ti.c fi~lds C'ferro_m.ruJnetic") ...

• Varieties .r!: Lodestone - Massive, magnetic variety of magnetite (acts as a magnet) :~ TItano-magnetite - Titanium-rich variety of magnetite ;~: Chrome-magnetite - Chromium-rich variety of magnetite

" In Group Oxides; Multigle oxides ; §~roup ,.

" All About The magnetic variety Lodestone only comes from a few areas. It is the only mineral that acts as a magnet. Although its magnetism is weak, it is strong enough to attract large nails. Due to its magnetic properties, very fine iron filings (usually originating from the mineral itself) cling to its surfaces.

Magnetite may form a yellow-brown fl:l.§.t coating if washed or kept in a moist area. If a specimen must by washed, it should be dried immediately. To prevent rusting, specimens should be stored in dry areas.

Hematite commonly forms Qseudomorphs over Magnetite. These pseudomorphs are known as Martite, and their appearance may be similar to regular Magnetite. However, they are only weakly attracted to magnetic fields, and have a reddish-brown streak.

" Uses Magnetite is an important ore of iron. Its perfect crystals are also famous among mineral collectors. This mineral is of scientific interest because of its special magnetic properties.

" Striking Features Strong attraction to magnets, llard ness, and streak

1/1 Popularity 2

1# Prevalence 1

" Demand 1

" Distinguishing tla.rtkUnit~ - only weakly attracted to magnetic fields Similar Minerals Spinel - not attracted to magnetic fields, has a white streak

Ilmenite - lighter streak GJJ.ro_mit~ - has a brownish streak

• Commonly g~lcite, Phlogopite, Talc, pyrite, Ilmenite, Hematite, 8QE1tite, Gamet, Chlorite Occurs With

" Noteworthy Magnetite is a common mineral, and exists in numerous localities. Only the finest are mentioned. Localities

_. Some famous worldwide occurrences are Binnental, Switzerland; Pfitschal, Tyrol, Austria; and the Palabora Mine, Transvaal, South Africa. The largest Magnetite deposits are in northern Sweden. Other enormous deposits are in Norway, Romania, and Russia. In the U.S., the magnetic variety Lodestone comes from the Iron Springs area (Dixie National Forest), Washington and Iron counties, Utah; and Magnet Cove, Hot Spring Co., Arkansas.

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Additional references

Large masses come from Franklin, Sussex Co., New Jersey, and perfect Q.QtaheJ1La1 cryStals m Chester, Windsor Co., Vermont. Interesting dodecahedral crystals were at one time

abundant at the Tilly Foster Mine, Brewster, Putnam Co., New York. Large cubic crystals occur in Balmat, St. Lawrence Co., New York, and the French Creek Mine, st. Peters, Chester Co., Pennsylvania has produced some large octahedrons. Large octahedrons were found in Monroe, Orange Co., New York and in Laurel Hill (Snake Hill), Secaucus, Hudson Co" New Jersey. Massive and poorly crystallized examples of this mineral

still be found in abundance in the dumps of the 19th century iron mines in the Ramapo ntains e and Rockland Counties, New York.

1. Clu~ter of .rusl~q .Magnetite .9ry!?tal~ 2. J;.t9.Dgr;lte~toQ.~~b~cJral crystal 3. Oc~ahedr~t cIY~tal

M~gnetic ~~~Qq~~~9n.e"

5. M etit~ in .. C.§l-'91t~ --- -_._----------------_. __ ..•... _ .. _._--_.-.

• The Mineral Gallery (Amethyst Galleries) • Min~[~logyJ;l.~t~Q~s~ (David Barthelmy) • ~lJs~n:~ut~ (Marc Favre)

JOHN BETTS

IJ,:t'r 111/1 • • H.rilr,'

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