Materials of the Earth’s crust 1The Geography Department 2011-12

Materials of the Earth’s crust

1The Geography Department 2011-12

Rocks are our world. The planet Earth is, essentially, just one big interesting rock, sometimes called "the third rock from the sun." The multi-faceted rock we live on supports life in many ways. The deep oceans, the vast deserts, and the high mountains, are just a few of the ways rock emerges and supports life.



What are rocks made up of ?


Rocks and minerals

A mineral is defined as a naturally occurring inorganic substance, which has definite physical properties and chemical composition. Eg. Quartz (SiO2), Feldspar (K2O.Al2O3.6SiO2), Mica (K4AlSi3O10(OH)2) etc are minerals.

A rock is defined as an aggregate or mixture of minerals.

Eg. Granite contains quartz, K-feldspar and K-mica. Marble contains Calcite (CaCO3) and Quartz.


Common Rock-forming minerals

1. Quartz –

2. Feldspar –

3. Mica –

4. Calcite –

5. Clay –


Quartz – Most common mineral;found in almost all rocks; shades of white, gray, and pink, mostly colourless with a glassy lustre.


FeldsparFound in rocks like granite and basalt; colour may

vary as K is replaced by Ca or Na. K-feldspar is pinkish or whitish while Ca and Na

feldspar is green or black


Micawhite or colourless flakes in granite and as black needles in basalt. K

may be replaced by Ca or Na.


Calcite – Occurs in rocks like limestone and marble. Colourless or white; crystalline or amorphous.


ClaySimilar to mica as it occurs as thin layers

differ as it has high water absorption capacity;

found in rocks like shale, conglomerate etc.


Hardness MineralAbsolute Hardness

1 Talc (Hydrated magnesium silicate) 1

2 Gypsum (Hydrated calcium sulfate) 2

3 Calcite (Calcium carbonate) 9

4 Fluorite (Used in toothpaste) 21

5 Apatite (Used in fertilizers) 48

6 Orthoclase 72

7 Quartz 100

8 Topaz 200

9 Corundum 400

10 Diamond 150012The Geography Department 2011-12

Types of rocks

Rocks are divided according to their origin into igneous, sedimentary and metamorphic rocks.


Igneous Rocks

Igneous Rock- rock that has been formed by the cooling and subsequent solidification of a molten mass of rock material, known as magma.

Depending upon the conditions under which the magma cooled, the resulting rocks may be coarse-grained or fine-grained.


Types of Igneous rocks

Any molten rock material is known as magma as long as it remains within the crust. If the magma erupts out of a volcano and spreads out on the surface of the earth, it is known as lava.

Besides, magma contains dissolved gases which are liberated once it comes out on the earth’s surface.

Based on the location where magma cools and solidifies, the resultant igneous rocks can be classified as follows.


Intrusive Igneous rocks

They are also called plutonic rocks. They are formed due to the cooling and

solidification of magma buried deep within the earth (in the magma chamber). A magma chamber that has cooled down and solidified is called a pluton.

Due to the lesser temperature difference between the magma and surrounding rocks, the magma cools down very slowly.

There is a lot of time for the mineral crystals to grow in size. As a result, the mineral crystals are large and visible and the resultant rock is crystalline or coarse-grained.

Examples-Gabbro & Granite


Extrusive igneous rocks

They are also called volcanic rocks.

They are formed due to the cooling and solidification of lava on the earth’s surface under atmospheric conditions.

Due to the greater temperature difference between the lava and atmosphere, the lava cools down very quickly.

There is very little time for the mineral crystals to grow in size. As a result, the mineral crystals are very small and the resultant rock is glassy or fine-grained.

Examples- Basalt & Rhyolite17The Geography Department 2011-12

Hypabyssal igneous rocks They are formed due to the cooling and

solidification of magma within the cracks and fissures of the surrounding rock.

The magma cools down at an intermediate rate, therefore the mineral crystals are

intermediate-sized and the resultant rock is medium-grained.

Structures formed due to the cooling and solidification of magma within the cracks and fissures of the surrounding rock are known as igneous intrusions. They may be of the following types.

a) Dyke – A wall shaped igneous intrusion, which cuts across the layers of surrounding sedimentary rocks.

b) Sill – A flat igneous intrusion that lies between two layers of sedimentary rock.

c) Batholith – An irregularly shaped igneous intrusion.



Sill Dike


TYPES OF IGNEOUS ROCKS

Basaltic magma Granitic magma

Extrusive or Volcanic

Basalt Rhyolite

Hypabyssal Dolerite Pegmatite

Intrusive or Plutonic Gabbro Granite


INTRUSIVE V/S EXTRUSIVE IGNEOUS ROCKS

GRANITE

GABBRO

PEGMATITE

• BASALT

•

• • RHYOLITE


Uses of igneous rocks

Granite and basalt are used extensively as building stones since they are very strong and durable.

Mica, which is used as an insulator and in lubricants, is found in pegmatite.

Basalt is also used as a road metal.


Sedimentary Rocks

Sedimentary rocks are so called because they are formed out of sediment, which is the term given to broken rock fragments.

DEPOSITION,

COMPACTION

CEMENTATION



Process of Sedimentation of rocks

a) Depositiona) In a low-lying area of the earth’s surface, usually the

continental shelf, river basin or a lake. The sediments are deposited in layers, also called stratified (stratum meaning layer) rocks.

b) Sand and Clay particles


b) Compactiona) the underlying sediments are subject to

pressure b) they tend to occupy the least possible volume.

Process of Sedimentation of rocks

c) Cementation –a) Rainwater dissolves atmospheric gases like carbon dioxide and

results into a weak carbonic acid. b) This carbonic acid takes the chemically weak minerals like

mica, calcite and feldspar into solution. c) This solution percolates through the sediment and occupies the

spaces between the rock fragments thereby cementing them. d) The rock fragments are bound together by calcium carbonate,

silica of iron oxide.

compaction + cementation = lithification. 27The Geography Department 2011-12


TYPES OF SEDIMENTARY ROCKS (DEPENDING ON HOW THEY HAVE BEEN FORMED)

SEDIMENTARY ROCKS

MECHANICALLY FORMED

ORGANICALLY FORMED

CHEMICALLY FORMED

MECHANICALLY FORMED: Formed out of fragments/pieces of other rocks.

Also called fragmental or clasticRunning water, wind and glaciers break

the rocks and deposit them into new sites.The processes of compaction and

cementation follow.Eg: Sandstone, clay, shale, conglomerate


TYPES OF SEDIMENTARY ROCKS

SANDSTONE

CLAY

SHALE

CONGLOMERATE

CHEMICALLY FORMED ROCKS: Limestone: May be formed by compaction and

cementation of shells in shallow parts of the continental shelf

Formed due to precipitation of minerals from a super-saturated solution. The water evaporates, the minerals crystallize and are compacted resulting into a rock.

Eg: Rock-salt or halite (Sodium Cloride under pressure in salt lakes or lagoons)

Gypsum (Calcium Sulphate from lakes and sea)Dolomite (Calcium magnesium from sea)


LIMESTONE

Accumulation of shells, shell fragments, or coral fragments, or by the crystallization of the mineral calcite from water.

PETROLEUM IS FOUND ALONG WITH DEPOSITS OF LIMESTONE

RO

CK

SA

LT

(HA

LITE

)

Rock Salt is a chemical sedimentary rock that forms from the evaporation of ocean or saline lake waters (Sodium Chloride). It is also known by the mineral name "halite".

GYPSU

M

It forms in lagoons where ocean waters high in calcium and sulfate content can slowly evaporate and be regularly replenished with new sources of water. associated with rock salt and sulfur deposits.

vast forest submerges underground and undergo changes like peat, lignite, coal (CARBONACEROUS

ROCKS)

Petroleum - Formed due to the decay of dead animals under marine water conditions like those in a continental shelf.


HOW COAL IS FORMED The coal we find today formed from generations of plants that died in ancient tropical swamps and accumulated on the swamp bottoms. The plant material first formed a compact organic material called peat. As layers of sediment gradually accumulated over the peat, the pressure and heat exerted by the thickening layers gradually drove out the moisture and increased the carbon content of the peat, forming coal.

Uses of sedimentary rocks

1. Rocks such as sandstone and limestone are widely used as building stones.

2. Sedimentary rocks contain deposits of important minerals like iron ore, manganese, bauxite,

gypsum, coal and petroleum.3. Fossils present in sedimentary rocks help

to determine the absolute and / or relative age of rocks.


Metamorphic rocks are formed when other rocks are subjected to intense heat (>600° C) and pressure (>150 Kilobars)

The rock that gets metamorphic undergoes changes in its structure (Layers/interlocked minerals ) as well as in its mineralogical composition.

Eg:Limestone turns into marbleCoal turns into GraphiteBasalt turns into Schist.

METAMORPHIC ROCKS

(Heat and Pressure)

The sources of heat and pressure

Heat – Magma, friction caused by the rubbing of lithospheric plates against each other

Pressure – Overlying sediments, rising magma, collision of lithospheric plates


Areas where metamorphic rocks are found

1. Near igneous intrusions

2. Mountain belts

3. Deep in the earth’s crust


Types of metamorphismContact metamorphismOccurs due to alteration of surrounding rocks by

magma, hence common near igneous intrusions.Area of rocks affected is very less, not beyond a

few hundred metres from the magma.Heat is the dominant agent of metamorphism


The Geography Department 2011-12 42

Types of metamorphism

Regional metamorphismOccurs due to movement of lithospheric

plates, hence common in mountain belts.Area of rocks affected is very large, often

thousands of square kilometres.Both heat and pressure play a

predominant role.


METAMORPHIC ROCKS

(Heat and Pressure)

LIMESTONE-MARBLE

METAMORPHIC ROCKS

(Heat and Pressure)

GRANITE- GNEISS

METAMORPHIC ROCKS

(Heat and Pressure)

SANDSTONE-QUARTZITE

METAMORPHIC ROCKS

(Heat and Pressure)

SHALE- SLATE

Agents of Metamorphism


Examples of metamorphic rocks

Schist



Gneiss



Marble



Basalt ------->SchistGranite ------->Gneiss (pronounced as ‘nice’)Shale ------->SlateSlate ------->SchistSandstone ------->QuartziteLimestone ------->MarbleCoal ------->Graphite

Take a Quizhttp://www.fi.edu/fellows/fellow1/oct98/expert/index.htmlhttp://www.kidsgeo.com/geology-games/rocks-game.php 52The Geography Department 2011-12

The Rock Cycle

Interactive rock cycle: http://www.learner.org/interactives/rockcycle/diagram.html53The Geography Department 2011-12

THE ROCK CYCLE


Rock Cycle The classic rock cycle illustrates the relationship between

the three main types of rock found on the Earth. In its simplest form, it demonstrates that igneous rock, which is formed by the cooling of magma, is in turn exposed to natural processes such as weathering, erosion, and compaction, creating sedimentary rock or exposed to heat and pressure, creating metamorphic rocks. The application of heat then turns sedimentary rock into metamorphic rock or exposure to agents of gradation converts them back into sediments, and further heating causes the metamorphic rocks to melt and in process to turn full circle, creating magma once more whereas further pressure can convert them into another metamorphic rock. However, the cycle does not necessarily have to pass through all these stages.


ORES AND GEMSTONES


ORES

A mineral is said to be an ore if it contains one or more elements, usually metals that

can be extracted from it in a profitable manner


ORES

Examples of minerals that are oresHaematite (Fe2O3) – Ore of Iron

Chalcopyrite (CuFeS2) – Ore of Copper

Magnetite (Fe3O4) – Ore of Iron

Galena (PbS) – Ore of LeadBauxite (Al2O3) – Ore of Aluminium

Sphalerite (ZnS) – Ore of ZincPyrolusite (MnO2) – Ore of Manganese


GEMSTONES

Gemstones are minerals that are treasured for their beauty and durability.

Their value generally depends on four features: The beauty of the stone itselfIts rarityIts hardness and toughnessThe skill with which it has been cut and

polished.59The Geography Department 2011-12

GEMSTONES


GEMSTONESMonth of birth Birthstone Colour

January Garnet Red

February Aquamarine Blue-green

March Amethyst Purple

April Diamond Colourless

May Emerald Green

June PearlMetallic white with a

play of colours61The Geography Department 2011-12

GEMSTONESMonth of birth Birthstone Colour

July Ruby Red

August PeridotHoney yellow or

green

September Sapphire Blue

October OpalMetallic white with a

play of colours

November Topaz Yellow

December TurquoiseBlue-green to greenish-grey62The Geography Department 2011-12

A quick RecapAnswer the following questions by clicking on

the right choice.If your answer is right you will move on to the

next question by clicking on the arrowIf your answer is not correct, you must go

back to the question by clicking on the arrow

Please do not skip any slideHave a nice time and fun learning.


Can wood be called a mineral?

Yes, it is naturally occurringNo, it does not have a chemical formulaYes, it has a fixed chemical formulaNo, its organic


OOPS!

That’s the wrong answer. Try Again


CORRECT!

Move on to the next question.


Mineral is to compound as Rock is to

ElementCompoundMixtureSolution


OOPS!



CORRECT!



Which of the following is NOT a correct point of difference between lava and magma?

Lava is found outside the earth while magma is found inside the earth.

Lava does not contain gases while magma contains gases.

Cooling of lava results in extrusive rocks while cooling of magma results in intrusive rocks.

Lava is less viscous (flows faster) ; magma is more viscous(moves slowly)


OOPS!



CORRECT!



Which of the following is NOT a characteristic of intrusive rocks?

They are dark in colour.They form inside the earth.They form due to slow cooling of magma.They have large crystals.


OOPS!



CORRECT!



Which of the following is a wall shaped igneous intrusion cutting across layers of sedimentary rocks?

SillDykeBatholithLaccolith


OOPS!



CORRECT!



Match the followingA Pegmatite 1 Basaltic equivalent of granite

B Gabbro 2 Hypabassal basaltic rock

C Rhyolite 3 Hyabassal granitic rock

D Dolerite 4 Extrusive rock of granitic composition

•A-2; B-1; C-4; D-3

•A-3; B-4; C-1; D-2

•A-3; B-1; C-4; D-2

•A-4; B-1; C-3; D-2


OOPS!



CORRECT!



Which of the following is the black coloured rock used as a kitchen platform?

BasaltLimestoneGraniteMarble


OOPS!



CORRECT!



Which of the following rocks is made up of well-rounded grains of quartz cemented together?

ShaleConglomerateLimestoneSandstone


OOPS!



CORRECT!



Which of the following rocks will form due to the evaporation and compaction of a super-saturated solution of calcium sulphate?

Rock SaltGypsumLimestoneDolomite


OOPS!



CORRECT!



Which process leads to the formation of limestone?

Compaction and cementation of shells in shallow parts of the continental shelf.

Dissolution of shells in the deep sea followed by super saturation and evaporation.

Dissolution of existing limestone by rainwater followed by deposition in underground caves and channels

All of the above.


OOPS!



CORRECT!



Which of the following is NOT TRUE about the formation of coal?

It forms in fresh water conditions.It forms due to decay of dead plants.It can also form due to decay of dead

animals.It requires a protective environment for its

formation.


OOPS!



CORRECT!



Which of the following is NOT TRUE about the formation of petroleum?

It forms only in marine conditions.Marine micro-organisms like

foraminifera are a must for its formation.After its formation, it remains at the

same place.It forms due to decay of dead bodies of

animals.97The Geography Department 2011-12

OOPS!



CORRECT!



Which of the following mineral is not found in sedimentary rocks?

Iron OreMicaBauxiteGypsum


OOPS!



CORRECT!



Which of the following is NOT TRUE about metamorphism?

It involves a physical change in the physical properties of a rock.

Minerals do not change.Even metamorphic rocks can be

metamorphosed.It may occur on account of heat or

pressure or both.


OOPS!



CORRECT!



Where can you find metamorphic rocks?

Near Igneous intrusions.Deep in the earth’s crust.Fold mountain belts.All of the above.


OOPS!



CORRECT!



Which of the following is not a metamorphic rock?

BasaltMarbleSchistGneiss


OOPS!



CORRECT!



Documents

Materials of the Earth’s crust 1The Geography Department 2011-12