Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term is a portmanteau of the words "magnesium" and "ferric". Most mafic minerals are dark in color and the relative density is greater than 3. Common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include basalt, dolerite 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 those in Hawaii.
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
Igneous rocks by composition Type Ultramafic
< 45% SiO2
>69 % SiO2
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mafic — [maf′ik] adj. [ MA(GNESIUM) + L f(errum), iron + IC] Geol. of or pertaining to igneous rocks that are rich in dark colored minerals and that contain magnesium and iron and a comparatively low level of silica … English World dictionary
mafic — ALASKA VOLCANO OBSERVATORY GLOSSARY An igneous composed chiefly of one or more dark colored minerals. GLOSSARY OF VOLCANIC TERMS A compositional term for igneous rocks which contain 45% 55% SiO2 (by weight). Mafic rocks are generally dark colored … Glossary of volcanic terms
mafic — adjective Etymology: New Latin magnesium + Latin ferrum iron + English ic Date: 1912 of, relating to, or being a group of usually dark colored minerals rich in magnesium and iron … New Collegiate Dictionary
mafic — /maf ik/, adj. Geol. of or pertaining to rocks rich in dark, ferromagnesian minerals. Cf. basic (def. 4), ultramafic. [1910 15; MA(GNESIUM) + L f(errum) iron + IC] * * * … Universalium
mafic — adjective Describing rocks, such as silicate minerals, magmas, and volcanic and intrusive igneous rocks, which contain relatively high concentrations of heavier elements … Wiktionary
mafic — [ mafɪk] adjective Geology relating to or denoting a group of dark coloured, mainly ferromagnesian minerals such as pyroxene and olivine. Often contrasted with felsic. Origin early 20th cent.: blend of magnesium and ferric … English new terms dictionary
mafic — maf·ic … English syllables
mafic — maf•ic [[t]ˈmæf ɪk[/t]] adj. pet gel of or pertaining to rocks rich in dark, ferromagnesian minerals • Etymology: 1910–15; ma(gnesium)+ L f(errum) iron + ic … From formal English to slang
mafic — /ˈmæfɪk/ (say mafik) adjective of some igneous rocks and their constituent minerals, composed dominantly of the magnesium rock forming silicates. Compare felsic … Australian English dictionary
mafic — ˈmafik adjective Etymology: magnesium + Latin ferrum + English ic more at farrier : of or relating to a group of minerals characterized by magnesium and iron and usually by their dark color … Useful english dictionary