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A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. 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 ...
Olivine. The mineral olivine (/ ˈɒl.ɪˌviːn /) is a magnesium iron silicate with the chemical formula (Mg, Fe)2 Si O 4. It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, [9] it is a common mineral in Earth's subsurface, but weathers quickly on the surface. Olivine has many uses, such as the ...
Petrology. Gabbro is a coarse-grained (phaneritic) igneous rock that is relatively low in silica and rich in iron, magnesium, and calcium. Such rock is described as mafic. Gabbro is composed of pyroxene (mostly clinopyroxene) and calcium-rich plagioclase, with minor amounts of hornblende, olivine, orthopyroxene and accessory minerals. [4]
Generally, the more silica is present in the rock, the fewer the mafic minerals, and the more sodium-rich the plagioclase. Alkali feldspar appears as the silica content becomes high. [ 28 ] Under the QAPF classification , plagioclase is one of the three key minerals, along with quartz and alkali feldspar, used to make the initial classification ...
Mafic rocks have a relatively low silica content and are composed mostly of pyroxenes, olivines and calcic plagioclase. These rocks (basalt, gabbro) are usually dark coloured, and have a higher density than felsic rocks. Ultramafic rock is very low in silica, with more than 90% of mafic minerals (komatiite, dunite).
Serpentinization is a form of low-temperature (0 to ~600 °C) [5] metamorphism of ferromagnesian minerals in mafic and ultramafic rocks, such as dunite, harzburgite, or lherzolite. These are rocks low in silica and composed mostly of olivine ((Mg2+, Fe2+)2SiO4), pyroxene (XY (Si,Al)2O6), and chromite (approximately FeCr2O4).
Solid solutions between albite and anorthite are called plagioclase, [11] or, more properly, plagioclase feldspar. Only limited solid solution occurs between K-feldspar and anorthite, and in the two other solid solutions, immiscibility occurs at temperatures common in the crust of the Earth. Albite is considered both a plagioclase and alkali ...
Mineralogy. Anorthite is the calcium-rich endmember of the plagioclase solid solution series, the other endmember being albite (NaAlSi 3 O 8). Anorthite also refers to plagioclase compositions with more than 90 molecular percent of the anorthite endmember. The composition of plagioclases is often expressed as a molar percentage of An%, or (for ...