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Igneous Rocks – From Fire. Igneous rock forms when lava or magma cools and hardens to form crystals (crystallization). Two Major Groups of Igneous Rocks – Classified according to where the rock crystallizes. Intrusive Igneous Rocks – when the cooling of magma occurs deep below the crust.
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Igneous Rocks – From Fire Igneous rock forms when lava or magma cools and hardens to form crystals (crystallization)
Two Major Groups of Igneous Rocks – Classified according to where the rock crystallizes • Intrusive Igneous Rocks – when the cooling of magma occurs deep below the crust. • Extrusive Igneous Rocks – when the rapid cooling of lava or melted rock occurs on the earth’s surface.
Texture – the size of the crystals in the rock. • Coarse grained – crystals can be seen with the naked eye • Fine grained – no visible crystals or the crystals are too small to be seen with the naked eye
Composition – the materials that form in igneous rocks depends on the chemical composition of the magma or lava from which the rock cools and crystallizes. • Felsic Igneous Rocks • fel = feldspar + sic = containing oxygen and silicon • Light in color • High in Silica • Main minerals are feldspar and quartz • Low Density • Mafic Igneous Rocks • Ma = magnesium + fic = ferric = iron • Dark in color • Low silica • High density