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Igneous Rocks

Igneous Rocks Formation of Igneous Rocks Igneous comes from the Latin word ignis , which means fire Intrusive igneous rocks are formed when magma hardens beneath Earth’s surface Extrusive igneous rocks are formed when lava hardens on Earth’s surface Classification of Igneous Rocks

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Igneous Rocks

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  1. Igneous Rocks

  2. Formation of Igneous Rocks • Igneous comes from the Latin word ignis, which means fire • Intrusive igneous rocks are formed when magma hardens beneath Earth’s surface • Extrusive igneous rocks are formed when lava hardens on Earth’s surface

  3. Classification of Igneous Rocks • Texture and composition are two characteristics used to classify igneous rocks • Texture describes the appearance of an igneous rock based on its size, shape, and arrangement of its interlocking crystals • Composition of igneous rocks are based on the proportions of light and dark minerals in the rock

  4. Texture • Coarse-grained texture is caused by slow cooling resulting in larger crystals • Fine-grained texture is caused by rapid cooling resulting in smaller, interconnected mineral grains Gabbro Andesite

  5. Texture continued • Glassy texture is caused by very rapid cooling • Porphyritic texture is caused by different rates of cooling resulting in varied sized minerals Obsidian (compact glass)

  6. Classification of Igneous Rocks • Composition of igneous rocks are based on the proportions of light and dark minerals in the rock • There are four types of composition • Granitic • Andesitic • Basaltic • Ultramafic

  7. Igneous Rock Summary • Igneous rocks form when magma or lava cools and hardens • Intrusive rocks form from magma deep within Earth • Extrusive rocks form from lava at Earth’s surface • Igneous rocks can be classified according to texture and composition

  8. Table 1 on page 74

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