IGNEOUS ROCKS by Charina Cameron Part 1: Classification & Composition

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