Chapter 4. Rocks. 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.
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Chapter 4 Rocks
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 Coarse grained • Texture involves 3 components: • Grain size • Grain shape • Grain pattern Fine grained Jagged grains Rounded grains banded Nonbanded
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.
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. Most common Extrusive rock Basalt Most common Intrusive rock Granite
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. This is called silt Can you see the shells? Sediments can be carried away by water to be deposited somewhere else.
From Sediment to Rock Step 3 Step 4 Steps 1 & 2
CLASTIC SEDIMENTARY ROCKS This is a breccia. Notice the jagged edges. This is sandstone. The individual fragments Are not easily seen. These are conglomerates This is shale, splits easily into thin sheets.
ORGANIC SEDIMENTARY ROCKS Limestone– forms in the ocean from shells, corals, calcite skeletons being compacted Coquina- a special type of limestone In which shells can be easily seen Coalis one of the most important organic rocks. Fossils are found mainly In sedimentary rocks.
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 located in Vietnam. These are called pancake rocks!
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 used In 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 Reef Australia
METAMORPHICROCKS • 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 layers Common examples: Slate, gneiss, schist • NONFOLIATED Grains 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.
NonfoliatedMetamorphic Rocks qUARTZITE MARBLE
USES OF METAMORPHIC ROCK All MARBLE
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.