Jun 6 2014
Mafic is a silicate mineral or rock, which is rich in magnesium and ferric oxides. It is composed of low amounts of potassium, aluminum, sodium, and silicon, and relatively high amounts of calcium, magnesium, and iron.
The word mafic was derived from its two constituent minerals - magnesium and ferric. This class of rocks crystallizes from silicate minerals at high temperatures.
Most mafic minerals, such as pyroxenes and olivines, are dark in color and have a relative density of greater than 3. Mafic rock is usually contrasted with felsic rock, which consists of light-colored minerals.
The most common mafic rocks include basalt and coarse-grained gabbro. Basalt is made of calcium-rich plagioclase and pyroxene, with small amounts of amphibole and olivine. It undergoes a Bowen reaction series, which is associated with mafic rocks. Basalt can also be observed with a porphyritic texture, which undergoes partial crystallization at depth, and an eruption at the surface.
The composition of gabbro is typically the same as that of basalt. However, gabbro has a different texture, with larger crystals formed deep inside the Earth’s surface. It can be considered an intrusive rock, with phaneritic texture. Its major constituents include pyroxene and calcium-rich plagioclase.
Mafic magmas are those that are separated from the upper mantle, and usually produced at the spreading centers. Mafic lava, on the other hand, has a low viscosity prior to cooling, owing to the lower silica content in mafic magma.
The eruptions of volcanoes raised from mafic lavas are less explosively violent when compared to felsic-lava eruptions. This is due to the fact that water and other volatile agents can easily escape from mafic lava. Most of the mafic-lava volcanoes are oceanic volcanoes, such as the volcanic eruptions in the Hawaiian Islands.
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