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Practical Earth Science

Lesson 8-2

Igneous Rocks

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Objectives

  • Explain how igneous rocks form.
  • Compare intrusive igneous rocks.
  • Identify samples of igneous rocks.

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Magma – hot, liquid rock inside the earth

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Intrusive rocks form underground from cooled magma

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Texture – Size of crystals in an igneous rock

Coarse-grained texture have large crystals

Mineral – Biotite Mica

Mineral - Quartz

Mineral – Muscovite Mica

Mineral - Feldspar

Mineral - Amphibole

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Extrusive Igneous Rock forms from lava

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Extrusive Igneous Rocks have a fine-grained texture because they cool very quickly. Some form glassy textures.

Obsidian can be made into arrowheads

Pumice floats

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Pahoehoe lava flows fast and is very liquidy and hot. It forms wrinkles.

Aa lava forms a surface of rough jaggled rocks.

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Coarse Grained Texture

Fine Grained Texture

Glassy Texture

Fracture Breakage Pattern

obsidian