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Classifying rocks � Rocks are made up of two or more 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 size 2) Grain shape 3) Grain pattern Fine grained Coarse grained Rounded grains Jagged grains 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. �
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How do Igneous Rocks Form? First rocks must melt into Lava/Magma! � Increase in Temperature – rocks melt � Decrease in Pressure – hot rock can remain solid if it is under high pressure deep within the Earth. When hot rock rises to the surface, the pressure goes down and rocks can melt. � Addition of Fluids – when fluids, such as water, mix with rock, the melting temperature of the rock decreases and the rock can melt.
IGNEOUS ROCKS Igneous rocks are classified according to their origin, texture, and mineral composition. � ORIGIN: Extrusive – formed from lava that has erupted (outside-”exit”). Intrusive – formed when magma hardens under the earth’s surface (inside). � Most common Extrusive rock Basalt Most common Intrusive rock Granite
Types of Magma/Lava Different compositions of lava or magma determine the types of igneous rocks formed. � Magma that contains sodium, potassium, and aluminum will form light colored called Felsic rocks such as granite. � � If the magma is high in iron, magnesium and calcium will form dark colored rocks called Mafic such as basalt.
Extrusive vs. Intrusive � Extrusive � Intrusive Rapid cooling � Small crystal size; fine grained � Can have a glassy texture � � Slow cooling � Larger crystals; coarse grained
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.
Borax Experiment � Final Observations �Trace two petri dish circles into your notebook. �Inside one circle draw what you see with the unaided eye. �Inside the second circle, draw what you see with the magnifying glass. �Describe the process we used to create these crystals. �How do these crystals compare with igneous rock creation?
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 • Particles are carried away by wind or water • Particles are deposited • DEPOSITION Erosion Steps 1 & 2 Step 3 Compaction • Particles are squeezed together by pressure • Particles are glued together as mineral solutions harden Cementatio n Step 4
Sedimentary rock formation
Formation under water The most noticeable feature of sedimentary rocks are layers called strata. Stratification is the process in which sedimentary rocks are arranged in layers.
Three Major Types of Sedimentary Rocks Clastic Organic • Rock formed by rock fragments that are cemented together; sometimes visible large fragments, sometimes small, fine fragments • Two common types are conglomerates, sandstone, breccias • Rocks formed by the remains of plants/animals that are cemented together. • Two common types are coal and limestone • Formed when minerals dissolved in water are crystallized when the water evaporates away Chemical • Calcite and Halite can form this way.
CLASTIC SEDIMENTARY ROCKS This is a breccia. Notice the jagged edges. These are conglomerates This is sandstone. The individual fragme Are not easily seen. This is shale, splits easily into thin sheets.
ORGANIC SEDIMENTARY ROCKS Limestone – forms in Coquina- a special type of lim the ocean from shells, In which shells can be easily see corals, calcite skeletons being compacted Fossils are found mainly In 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 formations These are called pancake rocks! These are located in Vietnam.
More limestone formations Here are some hot springs in limestone. Many cave formations are made of 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
Sedimentary Rock Experiment What are some similarities between the three samples? 2. What are some of the differences? 3. Are the grain sizes in the samples the same? 4. How would you describe the shapes of the grains you observe? 1.
Sedimentary Rock Experiment Closure 1. Draw a cycle, cartoon or some animation of your understanding of the formation of sedimentary rocks. Color your drawing if time permits. 2. Draw and label the layering of the sediments after they settle.
METAMORPHIC ROCKS (temps between 150 -1000 degrees � Heat celcuis) & 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.
Stories in Stone - Metamorphic Form 20 red and 20 blue small marble sized spheres. 2. Form the yellow clay into a pancake about the size of your hand. 3. Break the green in half and form 2 pancakes. 1.
Metamorphic Rock Experiment 1. 2. 3. 4. 5. 6. Observe and describe the layering in the piece of the model you just cut off. How was your fist similar to what happens when metamorphic rock is formed? How was your fist different? How is the piece of the model you “metamorphized” different from the piece you cut of that wasn’t “metamorphized”? Describe the metamorphic layers. How do metamorphic rocks differ from igneous or sedimentary rocks?
Two Types (textures) of Metamorphic Rocks �FOLIATED Rocks grains are arranged in parallel bands or layers Common examples: Slate, gneiss, schist �NONFOLIATE D Grains are arranged randomly. Common examples: Marble, quartzite
Non-foliated Metamorphic Rocks
With pressure, granite becomes gneiss (foliated rock). Igneous rock is changed to a metamorphic rock.
Increasing pressure causes greater foliation Increasing Pressure
SHALE SLATE SCHIST GNEISS
Index Minerals Some minerals, such as quartz, can form at many different temperatures. � Other minerals, such as garnet, form only at certain temperatures and pressures. � Therefore, rocks that contain minerals like garnet probably also formed at those temperatures and pressures and are called index minerals. � Index minerals and can indicate the temperature and pressure or depth at which a rock formed. �
Two ways rock can go through Metamorphism � Regional metamorphism – high pressures and temperatures cause the rock in a large area to change. It can happen where rock is buried deep below the surface or at convergent boundaries.
Two ways rock can go through Metamorphism 1. Contact metamorphism – rock is heated by nearby magma. The nearer the rock is to the magma, the more changes occur.
USES OF METAMORPHIC ROCK
World’s Largest Marble Quarry Tate, GA
Uses of SLATE
Rock Cycle Simulation 1. 2. 3. 4. 5. Where did you spend the most time? Why is the rock cycle called a cycle? Why did everyone not follow the same path? How does a rock become Igneous? Sedimentary? Metamorphic? Where are rocks being born and transformed today?
Rock Cycle Simulation Where are rocks being born and transformed today? 6. How much of the rock cycle can be observed? How much must be inferred? 7. How are people affected by movement of Earth material through the rock cycle? 8. If each step of our rock cycle game was 200, 000 years, what was the time period represented in the game? 5.
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. Click on the link for a Rock Cycle animation