Mafic

Mafic is an adjective describing a silicate mineral or igneous rock that is rich in magnesium and iron, and is thus a portmanteau of magnesium and ferric.[1] Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include basalt, diabase and gabbro. Mafic rocks often also contain calcium-rich varieties of plagioclase feldspar.

Basalt

Chemically, mafic rocks are enriched in iron, magnesium and calcium and typically dark in color. In contrast the felsic rocks are typically light in color and enriched in aluminium and silicon along with potassium and sodium. The mafic rocks also typically have a higher density than felsic rocks. The term roughly corresponds to the older basic rock class.

Mafic lava, before cooling, has a low viscosity, in comparison with felsic lava, due to the lower silica content in mafic magma. Water and other volatiles can more easily and gradually escape from mafic lava. As a result, eruptions of volcanoes made of mafic lavas are less explosively violent than felsic-lava eruptions.[2] Most mafic-lava volcanoes are shield volcanoes, like those in Hawaii.

Rock texture Name of mafic rock
Pegmatitic Gabbro pegmatite
Coarse grained (phaneritic) Gabbro
Coarse grained and porphyritic Porphyritic gabbro
Medium grained Diabase or dolerite, microgabbro
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 texture Tachylyte, sideromelane, palagonite

See also

References
  1. Schlumberger: Oilfield Glossary
  2. "Volcanoes". Columbia University. Retrieved 18 June 2019.
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