ROCKSChapter 4

Classifying rocks Rocks are made up of two or minerals. About 20 minerals make up most of the

earth’s rocks. When studying rocks, geologists

observe the mineral composition, color and texture of the rock.

This rock contains

three minerals.

Rock color A rock’s color can indicate the rock’s

mineral composition. Certain minerals are light in color while other minerals are dark in color.

Granites are usually light Basalts are usually dark

Rock Texture

Texture involves 3 components:

1) Grain size2) Grain shape3) Grain pattern

Fine grained Coarse grained

Rounded grains Jagged grains

Nonbanded banded

Three Groups of Rocks

Igneous – form from the cooling of magma or lava

Sedimentary – form when particles of rocks are pressed & cemented together

Metamorphic – when existing rocks are changed by heat, pressure, or chemical reactions.

This is NOT the correct answer!

IGNEOUS ROCKS Igneous rocks are

classified according to their origin, texture, and mineral composition.

ORIGIN:

Extrusive – formed from lava that has erupted.

Intrusive – formed when magma hardens under the earth’s surface.

Basalt

Granite

Most commonIntrusive rock

Most common Extrusive rock

Extrusive vs. Intrusive Extrusive Rapid cooling Small crystal size;

fine grained Can have a glassy

texture

Intrusive Slow cooling Larger crystals;

coarse grained

Types of Magma/Lava Different

compositions of lava or magma determine the types of igneous rocks formed.

Magma that contains SILICA will form light colored rocks such as

granite.

If the magma is low in silica will form dark colored rocks

such as basalt.

Uses of Igneous Rock Igneous rock has

been used for thousands of years for buildings and statues. Granite is the most widely used igneous rock.

SEDIMENTARY ROCKS Sediments are small bits & pieces of

rocks, shells, sand, bones, or parts of plants.

Can you see the shells?

This is called silt

Sediments can be carriedaway by water to be deposited somewhere else.

From Sediment to Rock

• Particles are carried away by wind or water• Particles are deposited• DEPOSITION

ErosionSteps 1 & 2

Step 3

Step 4

Sedimentary rock formation

Formation under water

Three Major Types of Sedimentary Rocks

Clastic

• Rock formed by rock fragments that are cemented together; sometimes visible large fragments, sometimes small, fine fragments

• Two common types are conglomerates, sandstone, breccias

Organic •Rocks formed by the remains of plants/animals that are cemented together.•Two common types are coal and limestone

Chemical •Formed when minerals dissolved in water are crystallized when the water evaporates away•Calcite and Halite can form this way.

CLASTIC SEDIMENTARY ROCKS

These are conglomerates

This is a breccia.Notice the jaggededges.

This is sandstone.The individual fragmentsAre not easily seen.

This is shale, splitseasily into thin sheets.

ORGANIC SEDIMENTARY ROCKS

Limestone – forms in the ocean from shells, corals, calcite skeletons being compacted

Coquina- a special type of limestoneIn which shells can be easily seen

Fossils are found mainlyIn sedimentary rocks.

Coal is one of the most important organic rocks.

The formation of COAL

Coal is made from once living plants & animals.

Limestone is formed from corals, and other sea animals.

These shells and animal remains get crushed and cemented together over time to form limestone.

Limestone formations

These are called pancake

rocks!

These are

located in

Vietnam.

More limestone formations

Many cave formations are

made of limestone.

Here are some hot springs in

limestone.

Chemical Sedimentary Rocks Gypsum and Halite are two of the most

common chemical sedimentary rocks. They can also be minerals! They formed by dissolved chemicals

crystallizing as water evaporates. For this reason they are sometimes

called EVAPORITES.

This is GYPSUM in a cave in New Mexico. Gypsum is Calcium Sulfate. It is usedIn plaster of paris, drywall, and Cement.

This is a chemical form of limestone. It is called TUFA.

Coral Reefs are responsible for much of the limestone on earth.

Coral is an animal much like a sea anenome. They have tentacles and eat plankton. To protect their soft bodies they secrete a hard substance called CALCITE. When they die, these calcite shells remain.

Ancient Coral Reef vs. Living Coral Reef

Great Barrier ReefAustralia

METAMORPHIC ROCKS Heat & pressure deep in the earth can change

any rock into a metamorphic rock. They can form from igneous, sedimentary and other metamorphic rocks.

Extremely high temps and pressures deep in the earth can actually change a rocks mineral composition.

Two Types of Metamorphic Rocks FOLIATED

Rocks grains are arranged in

parallel bands or layersCommon

examples:Slate, gneiss,

schist

NONFOLIATEDGrains are

arranged randomly.Common

examples:Marble, quartzite

Increasing pressure causes greater foliation

Increasing Pressure

SHALE SLATE SCHIST GNEISS

SEDIMENTARY

ROCK

With pressure, granite becomes gneiss. Igneous rock is changed to a metamorphic rock.

Nonfoliated Metamorphic Rocks

USES OF METAMORPHIC ROCK

World’s Largest Marble QuarryTate, GA

Uses of SLATE

The Rock Cycle

It is a series of processes

in the earth’s crust, mantle

and on the earth’s surface

that SLOWLY change

rocks from one kind to

another.