Rocks
Rocks are classified into three major groups. They are igneous, sedimentary, and metamorphic rocks. They are classified based on how they form.
Igneous Rock |
Igneous rock is a rock that forms from magma. They form when molten material cools and solidifies either inside Earth or at the surface. When they form inside the Earth, it is called an intrusive rock. On the other hand, when they form at the surface, the rock is called an extrusive rock.
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Intrusive Rock• Form underground
• Rich in iron and magnesium=dark color • Less dense=lighter color • Grow large underground, cool down slowly/corse-grained texture |
Extrusive Rock• Form at Earth's surface
• Cool very quickly=small crystals/fine-grained texture |
Magma• A mixture of molten rock and gases, including water vapor, which forms underground
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Lava• Magma that flows out of volcanoes
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Sediment |
Sediment consists of small, solid pieces of material that comes from rocks or living organisms.
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Sedimentary Rock |
Sedimentary rock is a rock that forms over time as sediment is squeezed and cemented. Sedimentary rock will also be classified into three groups. Clastic rocks, chemical rocks, and organic rocks are the three main groups and they are classified by their formation.
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Clastic Rocks• Form from the broken fragments of other rocks
• Held together by cement • Conglomerate=consists of gravel and pebbles • Breccia=made up of sharp edged fragments • Mudstone=primarily mud or silt • Shale=clay minerals are aligned, so it can split into sheets |
Chemical Rocks• Minerals precipitate out of solution
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Organic Rocks• The result of organic processes
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Metamorphic Rock |
Metamorphic rock is a rock that is changed by the temperature, pressure, or reactions with hot water. Rocks are transformed under high temperatures and pressure deep underground. Metamorphic rocks with crystals arranged in parallel layers or bands are called foliated rocks.
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Rock Cycle |
Rock cycle is a series of processes in which rocks continuously change from one type to another. For example, sedimentary rocks can be carried to the ocean. Then the rock will go back to the mantle due to the plate tectonics (explained in next section). This rock will become an igneous rock.
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