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Rock Notes. Igneous Rocks. Forms as Magma or Lava Cools. Two Types Intrusive: Forms underground in crust Cools very slowly so crystals have time to grow Looks spotted from crystals Extrusive: Forms on surface as lava cools Cools very quickly so no crystals
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Igneous Rocks • Forms as Magma or Lava Cools. • Two Types • Intrusive: Forms underground in crust Cools very slowly so crystals have time to grow Looks spotted from crystals • Extrusive: Forms on surface as lava cools Cools very quickly so no crystals has no crystals or is glassy or has air holes.
Sedimentary rocks Form as sediment (weathered rock) piles up and glues together. Two types • Clastic – forms when chunks of rock, mechanical weathering join together. • Chemical – forms when dissolved sediment is left behind when water evaporates.
Metamorphic rock • Form as any type of rock has heat and pressure applied to it.