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Igneous Rocks Properties and Identification Igneous - formed by crystallization from molten magma. Igneous rocks Sedimentary – I like this picture Mt. Baker is a volcano made of igneous rocks Rocks of the Vancouver Region C & T p. 20 Igneous Rocks Intrusive (Plutonic) Rocks – •Formed by slow crystallization deep beneath the Earth’s surface. •Large visible crystals – phaneritic •Identified by mineral content. Golden Ears, Maple Ridge. Extrusive (Volcanic) Rocks Formed by rapid crystallization on the Earth’s surface Crystals only visible under a microscope - aphanitic Identified by mineral content and structure Mt. Garibaldi, Squamish. Igneous Rocks Mineral Content Plutonic Rocks - Structure of Granite Polished granite section illustrating the mixture of large crystals of different minerals (q = quartz, af = albite feldspar, b = biotite mica Plutonic Rocks Granite - quartz, orthoclase, hornblende Diorite - orthoclase (Na & Ca), hornblende Granite - quartz, orthoclase, plagioclase, hornblende Gabbro - orthoclase (Ca), hornblende, pyroxene Bowen’s Reaction Series L L Silicon Content Viscosity L H H L Fe lds pa r gio c la s e Orthoclase (K) Feldspar Muscovite Quartz Resistance to Chemical Weathering (Sialic/Felsic) H Temperature Granite & Rhyolite Sodium rich Order of Crystallization (Intermediate) tit e Bio le ibo ph Am Diorite & Andesite e en (Mafic) rox Py Gabro & Basalt Calcium rich ne iv i (Ultramafic) Continuous Reaction Series Ol Peridotite Discontinuous Reaction Series Pla Rock Type H Correlation of Bowen’s Reaction Series with silicon content, viscosity of lava and relative resistance to chemical weathering Volcanic Rocks - Lavas Rhyolite (high Si) Basalt (high Fe) Andesite Basalt - vesicular More Volcanic Rocks Sodium Feldspar Basalt (Porphyry) Obsidian Calcium Feldspar basalt (Porphyry) Volcanic Breccia Volcanic Breccia - Kelowna Successive eruptions – Coal seams in between! Volcanic Rocks - Pyroclasts Pumice Welded Tuff Scoria Volcanic bomb - olivine core surrounded by basalt