igneous rocks by charina cameron part 1: classification & composition
TRANSCRIPT
IGNEOUS ROCKSby 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):
– rhyolite andesite basalt
• Plutonic igneous rocks (intrusives):
– granite diorite gabbro
GRANITE• Felsic magma
• Quartz Muscovite Biotite Hornblende Orthoclase
DIORITE• Intermediate magma
• Pyroxene
GABBRO
• Mafic magma
• Pyroxene Olivine Plagioclase
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 SiO2
• 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