The Online Encyclopedia and Dictionary







In geology, mafic minerals are silicate minerals, magmas, and volcanic and intrusive igneous rocks that have relatively high concentrations of the heavier elements. The term is a combination of "magnesium" and ferric, the Latin word for iron (III), but mafic magmas also are rich in calcium and sodium.

Mafic minerals are usually dark in color and have specific gravities greater than 3. Common rock-forming mafic minerals include olivine, pyroxene, amphibole, biotite and other micas, augite and the calcium-rich plagioclase feldspars. Common mafic rocks include basalt and gabbro.

In terms of chemistry, mafic rocks are on the other side of the rock spectrum from the so-called felsic rocks. The term roughly corresponds to the older basic rock class.

Rock Texture Name of Mafic Rock
Pegmatitic Gabbro pegmatite
Coarse grained (phaneritic) Gabbro
Coarse grained and porphyritic Porphyritic gabbro
Fine grained (aphanitic) Basalt
Fine grained and porphyritic Porphyritic basalt
Pyroclastic Basalt tuff or breccia
Vesicular Vesicular basalt
Amygdaloidal Amygdaloidal basalt
Many small vesicles Scoria
Glassy Tachylyte, sideromelane , palagonite

See also

Last updated: 05-13-2005 07:56:04