EXTRUSIVE IGNEOUS ROCKS Volcanoes and Volcanic Rocks Igneous Rock Names and Compositions Intrusive Volcanic Compositions Rock Name Rock Name Ultramafic Mafic Intermediate Silicic felsic Peridotite Gabbro Diorite Granite Komatiite Basalt Andesite Rhyolite MAGMA and LAVA Magma is the term for any molten silicate material whether below the surface or on top Volcanic rocks are erupted on the surface Volcanic rocks are fine grained 1 mm Lava is the term for a magma on the surface Low Viscosity High Temperature 1000 1200 C Normally Quiescent Lava Flows Aa early low temperature blocky flow Pahoehoe later high temperature ropy flow Pillow Lavas underwater flow Edifice Shields Cinder cones Higher viscosity higher polymerization Lower temperature Flows Viscous lava flows Pyroclastic flows Edifice Composite Cones Rhyolite Eruptions Very high viscosity Low temperature 600 800 C Massive Pyroclastic eruptions Air fall pumice Ash Flow Nu e Ardente Tuff Edifice Caldera 5 25 km Resurgent dome
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