Mafic is a term used in geology to describe a classification of igneous rocks that are rich in magnesium (Mg) and iron (Fe), as well as the minerals olivine, pyroxene, and amphibole. The term "mafic" is derived from the words "magnesium" and "ferric," which refer to the main elements found in these rocks. Mafic rocks are characterized by their dark color and dense composition. One of the main characteristics of mafic rocks is their high content of dark-colored minerals, such as pyroxene and amphibole. These minerals are known for their dark colors, ranging from black to dark green. This gives mafic rocks a dark appearance, which is why they are often called "dark rocks.
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Because of this abundance and because most igneous minerals are silicates, silica content was used as a basis of early classifications; it remains widely accepted today. Mafic rocks commonly found on the surface include basalt, pyroxene, and biotite; common ultramafic rocks are dunite and peridotite See also Earth, interior structure; Felsic; Sea-floor spreading.
This gives mafic rocks a dark appearance, which is why they are often called "dark rocks." In addition to their dark color, mafic rocks also have a dense composition. This is due to the high content of heavy elements such as magnesium and iron.
Mafic
Igneous rocks are classified by geologists using various schemes. One of the several schemes based on chemical composition divides igneous rocks into four categories according to silica (silicon dioxide, SiO2) content: (1) Rocks containing more than 66% silica are silicic . (2) Rocks containing 52 – 66% silica are classified as intermediate. (3) Rocks containing 45 – 52% silica are mafic. (4) Rocks containing less than 45% silica are ultramafic. The term acidic is sometimes used as a synonym for silicic and the terms basic and ferromagnesian as synonyms for mafic. Mafic is an invented adjective based on the chemical symbols for magnesium (Ma) and iron (Fe): Ma-Fe-ic, mafic. Mafic is sometimes used as a synonym for "darkcolored" when discussing the appearance of minerals . Some mafic and ultramafic rocks are found on Earth's surface. However, because magnesium and iron are denser than silica, mafic rocks are denser than silicic rocks and tend to sink below them. This density difference explains the dependence of Earth's composition on depth. Earth's core consists mostly of fairly pure metal (iron and nickel); surrounding the core is the mantle, a layer consisting mostly of ultramafic rock (metals mixed with silica). The outermost layer of the earth, the crust , consists of two basic types of crust, one primarily mafic (oceanic crust) and the other primarily silicic (continental crust). Oceanic crust, which is only about 4 miles (6 km) thick, consists mostly of basalt , a mafic rock. As oceanic crust inches away from its point of origin at a mid-ocean ridge, its underside cools the ultramafic mantle rocks over which it slides. These cooled mantle rocks stick to the underside of the oceanic crust, thickening it over time. The oceanic crust is thus weighed down by an increasingly thick undercoating of cooled ultramafic mantle rock as it ages. This cool undercoating is denser than the chemically identical but hotter mantle rocks below. Eventually it becomes heavy enough to drag the oceanic crust right down into the mantle, as occurs at a spontaneous subduction zone . The continents, in contrast, are silicic, and float permanently on the mantle. Mafic oceanic crust is spontaneously subducted into the mantle after at most 200 million years, while the continents have never been subducted in the three or four billion years since they were formed. By weight, Earth consists mostly of mafic and ultra-mafic rocks, but silicic rocks are far more abundant on Earth's surface. Mafic rocks commonly found on the surface include basalt, pyroxene, and biotite; common ultramafic rocks are dunite and peridotite See also Earth, interior structure; Felsic; Sea-floor spreading
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The presence of these elements, along with the dense minerals they form, gives mafic rocks a high specific gravity. This means that mafic rocks are heavier than rocks with a lower content of magnesium and iron. Mafic rocks are typically formed in volcanic environments, where they are produced by the cooling and solidification of magma. The magma from which mafic rocks form is known as basaltic magma. Basaltic magma has a relatively low viscosity, which allows it to flow easily and reach the Earth's surface. As a result, mafic lava can travel large distances before solidifying, forming expansive lava flows. The classification of rocks as mafic depends on their mineral composition. In order to be classified as mafic, a rock must contain at least 45% mafic minerals, such as olivine, pyroxene, or amphibole. Rocks that contain less than 45% mafic minerals are classified as intermediate or felsic, depending on their mineral composition. Mafic rocks have a number of practical uses. Due to their dense composition and resistance to weathering, they are often used as construction materials. For example, basalt, a common mafic rock, is widely used as a building material for roads, pavements, and buildings. Mafic rocks are also used as a source of crushed stone, which is used in the production of concrete and asphalt. In conclusion, mafic rocks are igneous rocks that are rich in magnesium and iron, as well as dark-colored minerals such as pyroxene and amphibole. These rocks are characterized by their dark color and dense composition. They are typically formed in volcanic environments and have a number of practical uses..
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