GEO 303 Igneous Rocks

Felsic

Igneous rock rick in light colored minerals such as feldspar

Mafic

Igneous rock rick in dark colored ferromagnesian minerals (augite, hornblende) and plagioclase feldspar

Ultramafic

Igneous rock composed of dark colored ferromagnesian minerals (olivine and pyroxene)

Ferromagnesian

Silicate minerals (olivine, augite, hornblende, and biotite) with Fe and Mn

Extrusive

• cools above Earth’s surface

• smaller crystals

• fast cooling

Intrusive

• cools beneath Earth’s surface

• larger crystals

• slow cooling

Aphaneritic

Fine-grained

Phaneritic

Coarse-grained

Pegmatitic

large crystals

Vesicular

Porous igneous rock

Porphyritic

Mixture of large and small crystals

Glassy

no minerals

peridotite

• ultramafic

• phaneritic

• slow-cooling

• olivine & pyroxene

scoria

• mafic

• vesicular

• fast-cooling

• pyroxene, plagioclase, & olivine

granite

• felsic

• phaneritic

• slow-cooling

• k-feldspar, muscovite, quartz

granite pegmatite

• felsic

• pegmatitic

• slow-cooling

• k-feldspar, muscovite, quartz

pumice

• felsic

• vesicular

• fast-cooling

• k-feldspar, muscovite, & quartz

andesite

• intermediate

• porphyritic

• slow → fast cooling

• amphibole, biotite, & plagioclase

basalt

• mafic

• aphanitic

• fast-cooling

• pyroxene, plagioclase, & olivine

rhyolite

• felsic

• aphanitic

• fast-cooling

• k-feldspar, muscovite, & quartz

obsidian

• felsic

• glassy

• fast-cooling

• NO MINERALS

gabbro

• mafic

• phaneritic

• slow-cooling

• pyroxene, plagioclase, olivine