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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 ...
Peridotite, a type of ultramafic rock. Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are usually composed of greater than 90% mafic minerals (dark colored, high magnesium and iron content).
In some modern literature, the term variole is defined as a type of spherulite that occurs in a mafic rock. However, because several different mechanisms can produce these small-scale, light-colored, globular to spherical structures, a specific set of varioles may or may not be spherulites that are composed of radiating crystals of either ...
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 ( (Mg 2+ , Fe 2+ ) 2 SiO 4 ), pyroxene ( XY(Si,Al) 2 O 6 ), and chromite (approximately FeCr 2 O 4 ).
These rocks (diorite, andesite) are typically darker in colour than felsic rocks and somewhat more dense. 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 ...
Humanity has made use of rocks since the earliest humans. ... Most rocks contain silicate minerals, compounds ... which is an igneous rock of mafic composition ...
Rocks with low color indices are felsic, and those with higher color indices are mafic, [6] although the exact thresholds used vary. This terminology conflicts with the definition [7] [8] of felsic and mafic rocks based on silica content. [6] For example, a rock composed entirely of pyroxene would contain about 50% silica. [6]
Quartzolite – Extremely rare igneous rock made mostly of quartz – An intrusive rock composed mostly of quartz; Rhyodacite – Volcanic rock rich in silica and low in alkali metal oxides – A felsic volcanic rock which is intermediate between a rhyolite and a dacite; Rhyolite – Igneous, volcanic rock, of felsic (silica-rich) composition