Igneous Rocks - rocks form from it ii For(pretty much all...

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Igneous Rocks – Chapter 3 Notes I. What is a rock? a. Rock is a naturally formed, consolidated material made of one or more types of minerals i. Sand, cement – not rocks II. What is an Igneous Rock? a. A rock formed from magma III. Two markers of Igneous Rock a. Physical texture i. Igneous Rock Textures 1. Extrusive rocks cooled on the surface a. Cooled quickly (in air or water) b. Small mineral grains i. Obsidian 2. Intrusive rocks cooled underground a. Cooled slowly, so big grains – Granite i. Intrusive bodies 1. Intrusive 2. Dikes (crack) & sill (layer) 3. Igneous Rocks a. Hawaii is made out of basalt, an igneous rock b. Basalt is a fine grained because it is extrusive c. Torres are made out of granite d. Granite is a course-grained because it’s intrusive 4. Porphyritic texture (phenocrysts & groundmass) a. Two rates of cooling b. Chemical composition i. The chemical composition of magma determines what type of
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Unformatted text preview: rocks form from it ii. For (pretty much) all rocks, Silicate (SiO2) is the major components 1. Siliac (felsic) rocks – light colored a. Felsic rocks are high in silicates – 65% or more silicate by weight b. Low in metals 2. Mafic rocks (Magnesium-Iron –ic) – dark colored a. Low in silicate (about 50% in weight) b. Replaced in magnesium, iron and calcium 3. Ultramafic rock a. Superlow amounts of silicate (45% or lower) i. Basalt – fine-grained – mafic – extrusive ii. Granite – course-grained—felsic—intrusive iii. Rhyolite—fine-grained—felsic—extrusive iv. Gabbro—course-grained—mafic—intrusive IV. Igneous rock distribution a. Under land – felsic and light b. Under oceans/islands – mafic and heavy...
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