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Igneous Rocks

Igneous Rocks. What is an Igneous Rock?. Igneous rocks are rocks formed when molten rock cools and solidifies. There are two terms used for molten rock. MAGMA. Molten rock inside the Earth is called magma.

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Igneous Rocks

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  1. Igneous Rocks

  2. What is an Igneous Rock? • Igneous rocks are rocks formed when molten rock cools and solidifies. • There are two terms used for molten rock.

  3. MAGMA • Molten rock inside the Earth is called magma. • Once formed, magma rises toward the surface because it is less dense than the surrounding rocks.

  4. LAVA • Lava is the word for magma when it erupts onto the Earth's surface.

  5. 2 Types of Igneous Rocks • Intrusive Igneous Rocks: • Form beneath Earth’s surface • Cool slowly • Large crystals

  6. 2 Types of Igneous Rocks • Extrusive Igneous Rocks: • Form on Earth’s surface • Cool quickly • Small crystals • Sometimes no crystals

  7. Classification is based on crystal size and composition.

  8. Crystallization • The formation and growth of a crystalline solid from a liquid or gas. • Remember the crystal shapes we discussed for properties of minerals.

  9. Types of Igneous Textures Aphanitic Phaneritic Porphyritic Glassy Pyroclastic Pegmatitic

  10. Aphanitic/Phaneritic • Aphanitic • Rapid cooling • Small crystals • Fine –grained texture • Extrusive rock • Phaneritic • Slow cooling • Large crystals • Coarse-grained texture • Intrusive rock

  11. Porphyritic/Glassy • Porphyritic • Contains large and small crystals in one rock. • Due to certain minerals crystallizing quicker than others. • Glassy • Rapid cooling • No crystals • Looks like glass • Extrusive rock

  12. Pyroclastic/Pegmatitic • Pyroclastic • Clumps of rock fragments • Form from volcanic rock • Pegmatitic • Exceptionally coarse-grained texture • Formed from a fluid-rich environment • Crystals all larger than 1cm

  13. Igneous Compositions: Granitic composition Basaltic composition Composed of dark colored silicates. Ex. ferromagnesian minerals -Make up the oceanic crust • Composed of light colored silicates. • Ex. quartz and feldspar -Make up the continental crust

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