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Published byChad Cunningham Modified over 9 years ago
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IGNEOUS ROCKS
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I.Igneous rocks are formed from molten material. - The term igneous is derived from Latin term meaning “from FIRE”!!
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A. Extrusive igneous rocks are formed when molten rock cools above ground. Usually they are formed after the material has been erupted by a volcano. 1.This molten material cools quickly. 2.No crystals are visible to the eye. ENVIRONMENT
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B.Intrusive igneous rocks are formed when molten rock cools below ground. 1.These rocks cool very slowly. 2.There is lots of time for visible crystals to grow
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Cools quickly Cools slowly Cools above ground Cools below ground No visible crystals Visible crystals EXTRUSIVEINTRUSIVE
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TEXTURE Coarse : –INTRUSIVE igneous rock composed of large mineral grains. GRANITE
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TEXTURE Fine : –EXTRUSIVE igneous rock composed of fine-grained minerals. BASALT
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TEXTURE Glassy : –HIGHLY VISCOUS, silica-rich magma cools rapidly, no crystals. OBSIDIAN
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TEXTURE Vesicular : –HIGHLY VISCOUS, large amount of dissolved gases, rock full of holes. PUMICE
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COMPOSITION Mafic : –Low silica –Rich in Iron and Magnesium DARK COLOR. BASALT
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COMPOSITION Felsic : –High silica LIGHT COLOR. RHYOLITE
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Igneous Rock Structures Intrusions vs. Extrusions : - Form Underground - Form on the surface of the Earth
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INTRUSIONS Batholiths : –At least 100 km 2 of surface exposure. Means “Deep Rock” Sierra Nevada Mountains
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Exposed Batholiths
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INTRUSIONS Laccoliths : –Flat-bottom intrusion that pushes over- lying rock layers into an arc. Means “Lake of Rock” Black Hills –South Dakota
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INTRUSIONS Stocks : –Like a Batholith, but covers less than 100 km 2. Devils Tower –Wyoming
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INTRUSIONS Dikes : –Igneous intrusion that cuts across rock layers. Black Canyon –Colorado
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INTRUSIONS Sills : –Hardened magma formed between parallel layers of rock. Salisbary Crags –Scotland
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EXTRUSIONS Volcanic Necks : –Solidified central neck of a volcano. Shiprock –New Mexico
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