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.