Mafic
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Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron. Most mafic minerals are dark in color and the specific gravity is greater than 3. Common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include basalt and gabbro.
In terms of chemistry, mafic rocks are on the other side of the rock spectrum from the felsic rocks. The term roughly corresponds to the older basic rock class.
Mafic lava, before cooling, has a low viscosity, in comparison to felsic lava, due to the lower silica content in mafic magma. Water and other volatiles can more easily and gradually escape from mafic lava, so eruptions of volcanoes made of mafic lavas are less explosively violent than felsic lava eruptions. Most mafic lava volcanoes are oceanic volcanoes, like Hawaiʻi.
| 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 |
