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Igneous rocks are formed as the lava cools above ground.

CLASSIFYING ROCKS We can also use the characteristics of rocks to classify them. Geologists separate rocks into three main categories based on how they were formed: igneous , metamorphic and sedimentary.

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Igneous rocks are formed as the lava cools above ground.

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  1. CLASSIFYING ROCKSWe can also use the characteristics of rocks to classify them. Geologists separate rocks into three main categories based on how they were formed: igneous, metamorphic and sedimentary.

  2. Rocks on the earth's surface are subject to the processes of erosion which are continually breaking down and being rearranged. Sedimentary rocks can be formed from metamorphic, igneous or other sedimentary rocks that have been broken down or broken up by weathering and erosion. In nature sedimentary rocks are usually layered.

  3. Igneous rocks are formed as the lava cools above ground. As these pockets of magma cool slowly underground, the magma becomes igneous rocks.

  4. Underground, they are formed when the melted rock, called magma, deep within the earth becomes trapped in small pockets.

  5. When magma appears above the earth, it is called lava.

  6. These rocks are sedimentary. Can you see the layering?

  7. Rocks that have changed shape or composition due to intense heat and pressure are called metamorphicrocks. Metamorphic rocks are created from sedimentary, igneous or other metamorphic rocks. • They are formed deep inside the earth. Heat, and pressure from the rock above flatten and bend the rock or even exchange atoms, forming new minerals.

  8. Deposition is simply when rocks, sand, or other materials are deposited in an area a natural process like a river flowing. What type of change is this? Physical Why?

  9. Wedging is when rocks are split apart by water. The water fills the gap, then freezes and pushes the rock apart, then melts and the gap in the rock is larger. What type of change is this? Why? Physical See TAKS workbook, pages 236 - 237

  10. Sometimes the rocks are packed tightly together. We call this cementation. What type of change is this? Why? Physical

  11. Small rocks, fragments and organic remains that have been moved by water, wind or other agents of weathering and erosion are called sediment. Over a period of time, sediment is pressed or cemented together to form sedimentary rocks.

  12. Erosion occurs when the earth’s surface is worn away by the action of water and wind. What type of change is this? Why? Physical

  13. Heat and pressure can actually change rocks into another substance. It takes a lot of heat and pressure to do this. What type of change is this? Chemical Why?

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