AIM: How do

Rocks Tell Stories?

Do Now: What are the three different types of rocks? How are they

formed?

Igneous rocks …

formed from cooling

and solidification of

lava or magma

Rock Classification – 3 major

groups based on their methods of

formation or origin

Rock Types

• Sedimentary

rocks …

from compacted

and cemented

sediments, or

chemical

precipitates or

evaporites

• Metamorphic

rocks-

meta = change

morphic = form

rocks changed by

heat and pressure

–but remain solid

IGNEOUS ROCKS

Magma – molten material

BELOW the surface of the

Earth

Lava – molten material

AT OR ABOVE earth’s

surface

MAGMA VS. LAVA

VOLCANO - landforms generated when lava is

released from the Earth’s interior through

openings.

EXTRUSIVE FEATURES

Magma Intrusive

Features - Plutonic

Classification of Igneous Rocks

by Texture

• WHAT IS TEXTURE?

It is not how it feels

SIZE OF MINERAL CRYSTALS

INTERGROWN SILICATE

CRYSTALS - RANDOM PATTERN

What controls texture?

How fast an igneous rock

cools.

What controls how fast an igneous

rock cools?

Where the rock is formed.

coarser crystals

slower cooling

deep in ground

EXTREMELY SLOW COOLING HAS

ABNORMALLY LARGE CRYSTALS

AND IS VERY COARSE.

INTRUSIVE – MAGMA

Granite Rhyolite Figure 4.7 A MINERAL COMPOSITION THE SAME – TEXTURE ONLY DIFFERENCE

Intrusive vs. Extrusive

INTRUSIVE EXTRUSIVE

Diorite Andesite

Figure 4.7 B

MINERAL COMPOSITION THE SAME ---- TEXTURE ONLY DIFFERENCE

Intrusive vs. Extrusive

INTRUSIVE EXTRUSIVE

Gabbro Basalt MINERAL COMPOSITION THE SAME – TEXTURE ONLY DIFFERENCE

Intrusive vs. Extrusive

INTRUSIVE EXTRUSIVE

SEDIMENTARY ROCKS

Sedimentary Rocks

• 80 % of Earth’s surface is covered

with sediments and Sedimentary

Rocks

What is sediment????

Broken pieces of rocks called CLASTS

Chemical precipitates ( dissolved solids

come out of solution)

Organic fragments – shells, decayed

plant matter – this is called BIOCLASTIC

Source of Sediment

When Igneous, Metamorphic Rocks, and

Sedimentary Rocks are uncovered and exposed

to the atmosphere and hydrosphere they start to

break down

Weathering is the general term for all actions

that break down or wear away rock

Erosion is the carrying away of the sediment

The four steps to the formation of

sedimentary rocks are:

1. Deposited in horizontal layers

called beds or strata

2. Buried

3. Compacted – particles forced

extremely close together because

of the pressure of the overlying

layers and water

4. Cemented – glued together

Sedimentary Rocks Sediments that are

eroded settle to the bottom of the rivers, lakes, and oceans

Layer after layer of eroded earth is deposited on top of each other

Sand Composition Varies BUT TO BE

CONSIDERED SAND THE GRAIN SIZE IS

BETWEEN 0.2 -0.006 CM.

Breccia

Sediments

are

pebbles,

cobbles,

and

boulders

rounded

angular

Sand (0.2 to 0.006 cms.)

SANDSTONE

Silt (0.006 to 0.0004 cms.

SILTSTONE

Clay (less than 0.0004 cms.)

SHALE

ROCK SALT

DOLOSTONE

ROCK GYPSUM

Intergrown

crystals of just

1 mineral

BIOCLASTIC LIMESTONE CHEMICALLY PRECIPITATED

LIMESTONE

COAL

Cretaceous Limestone Deposits in Kansas

HORIZONTAL LAYERS

METAMORPHIC ROCKS

METAMORPHIC ROCKS META = CHANGE MORPH = FORM

Called the “Cinderella Rock”

Start with pre-existing rock

and change to another rock –

but these changes occur in the

SOLID STATE

METAMORPHISM

Process by which igneous,

sedimentary, or another

metamorphic rock called the

“parent rock” undergoes

changes in minerals and

texture

METAMORPHISM

Occurs in rocks due to the

effects of

• High temperature

• High pressure

HEAT EFFECTS

Temperature increases with depth or contact with magma

Random

arrangement

of minerals

Organized

arrangement of

minerals - banding

METAMORPHIC ROCK MANTRA

• INTERGROWN CRYSTALS

IN AN ORGANIZED

PATTERN

FOLIATED METAMORPHIC ROCKS

MICA

CRYSTALS

BECOME

LARGE

AND

SPANGLY

MICA SCHIST WITH GARNET

DEFORMED GNEISS

SANDSTONE METAMORPHOSES INTO QUARTZITE