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IGNEOUS ROCKS. I.Igneous rocks are formed from molten material. - The term igneous is derived from Latin term meaning “from FIRE”!!

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Presentation on theme: "IGNEOUS ROCKS. I.Igneous rocks are formed from molten material. - The term igneous is derived from Latin term meaning “from FIRE”!!"— Presentation transcript:

1 IGNEOUS ROCKS

2 I.Igneous rocks are formed from molten material. - The term igneous is derived from Latin term meaning “from FIRE”!!

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4 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

5 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

6 Cools quickly Cools slowly Cools above ground Cools below ground No visible crystals Visible crystals EXTRUSIVEINTRUSIVE

7 TEXTURE Coarse : –INTRUSIVE igneous rock composed of large mineral grains. GRANITE

8 TEXTURE Fine : –EXTRUSIVE igneous rock composed of fine-grained minerals. BASALT

9 TEXTURE Glassy : –HIGHLY VISCOUS, silica-rich magma cools rapidly, no crystals. OBSIDIAN

10 TEXTURE Vesicular : –HIGHLY VISCOUS, large amount of dissolved gases, rock full of holes. PUMICE

11 COMPOSITION Mafic : –Low silica –Rich in Iron and Magnesium DARK COLOR. BASALT

12 COMPOSITION Felsic : –High silica LIGHT COLOR. RHYOLITE

13 Igneous Rock Structures Intrusions vs. Extrusions : - Form Underground - Form on the surface of the Earth

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15 INTRUSIONS Batholiths : –At least 100 km 2 of surface exposure. Means “Deep Rock” Sierra Nevada Mountains

16 Exposed Batholiths

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18 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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20 INTRUSIONS Stocks : –Like a Batholith, but covers less than 100 km 2. Devils Tower –Wyoming

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22 INTRUSIONS Dikes : –Igneous intrusion that cuts across rock layers. Black Canyon –Colorado

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24 INTRUSIONS Sills : –Hardened magma formed between parallel layers of rock. Salisbary Crags –Scotland

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26 EXTRUSIONS Volcanic Necks : –Solidified central neck of a volcano. Shiprock –New Mexico


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