IGNEOUS ROCKS by Charina Cameron Part 1: Classification & Composition

CLASSIFICATION Based on –Composition Magma type –Felsic = granitic –mafic = basaltic Minerals present –quartz, K-feldspar, plagioclase, mafic minerals, etc. –Texture Reflects magma cooling and crystallization history Finely crystalline is usually volcanic Coarsely crystalline is usually intrusive –Place of origin Plutonic or intrusive Volcanic or extrusive

PLUTONIC vs VOLCANIC Volcanic igneous rocks (extrusives): –rhyoliteandesitebasalt Plutonic igneous rocks (intrusives): –granitedioritegabbro

GRANITE Felsic magma Quartz Muscovite Biotite Hornblende Orthoclase

DIORITE Intermediate magma Pyroxene

GABBRO Mafic magma Pyroxene OlivinePlagioclase

ULTRAMAFIC ROCKS Dunite Peridotite Pyroxenite Amphibolite (Hornblende)

PEGMATITES Coarse textures (phaneritic) Usually granitic in composition Crystallized from hot residual fluids from magma May contain –very large crystals –unusual minerals

SOME PEGMATITE MINERALS Quartz & Orthoclase Biotite, Quartz, & Orthoclase Tourmaline crystals (black) in Orthoclase

SILICA CONTENT OF MAGMAS Silica is SiO 2 Refers to Si and O found in silicate minerals

PROPERTIES OF MAGMAS

BOWEN'S REACTION SERIES 2 branches: –Discontinuous –Continuous Residuals: –K-feldspar (orthoclase) –Muscovite –Quartz