Rock Types

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  • Types of Rock
    • Igneous Rocks
      • Formed from magma that's cooled down
      • Intrusive igneous rocks
        • 1. form when magma cools down below earth's surface
          • 2. magma cools down very slowly, forming large crystals - give rocks coarse texture
            • 3. large domes of cooled magma form domes of igneous rock - batholiths
              • 4. where magma has flowed into gaps in surrounding rock it forms dykes and sills
      • extrusive igneous rocks
        • 1. form when magma cools down after erupted from a volcano onto earth's surface
          • 2. magma cools down very quickly, forming small crystals that give the rocks a fine texture
      • composed of interlocking crystals - generally tough rocks & resistant to erosion
    • Sedimentary Rocks
      • formed when layers of sediment are compacted together until they become solid rock
      • usually form layers called beds
      • often contain fossils
      • although some rocks are tough, most weaker than igneous & metamorphic rocks
    • Metamorphic rocks
      • formed by heat and pressure
      • 1. rocks deep in the earth are changed by pressure from the weight of material above them
        • when tectonic plates collide, rocks are changed by massive heat & pressure that builds up
          • 3. magma from mantle heats the rocks in crust, causing them to change
      • crystalline
      • often exibit layering called cleavage & banding
      • tend to be very tough & resistant to erosion

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