Common mafic rocks include basalt and gabbro. Please note that some geologists with questionable motives switch the order of the magnesium and iron and come up with the term "femag. Felsic, on the other hand, is used for silicate minerals, magmas, and rocks which have a lower percentage of the heavier elements, and are correspondingly enriched in the lighter elements, such as silicon and oxygen , aluminum, and potassium.
The term comes from FEL for feldspar in this case the potassium-rich variety and SIC, which indicates the higher percentage of silica. Felsic minerals are usually light in color and have specific gravities less than 3. Common felsic minerals include quartz, muscovite mica, and the orthoclase feldspars.
The most common felsic rock is granite , which represents the purified end product of the earth's internal differentiation process. They cool too quickly to form crystals. Glasses do not have an orderly arrangement of atoms and there are therefore no minerals, in the strict sense, in them.
Felsic minerals quartz, K feldspar, etc are light colored while mafic minerals hornblende, pyroxenes are normally dark colored. Feldspars crystallize from magma as both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock. Rock formed almost entirely of calcic plagioclase feldspar is known as anorthosite. Feldspars are also found in many types of sedimentary rocks. It is also determined by the rate that the magma cools. If the magma cools deep underground, it cools slowly.
If the magma cools at or very near the surface, it cools quickly. This results in two different rock types. Mafic igneous rocks are iron and magnesium rich and contain abundant pyroxene, and calcium rich plagioclase feldspar.
Mafic igneous rocks are dark or black in color. Igneous rocks that crystallize at high temperatures contain calcic plagioclase rich in calcium , and rocks forming at lower temperatures contain sodic plagioclase rich in sodium.
A partly crystallized magma is separated into a solid rock containing calcic plagioclase and a still molten residue richer in sodium. Felsic rocks Rocks composed mostly of biotite, muscovite, sodium-rich plagioclase feldspars, potassium feldspars, and quartz make up the felsic family of igneous rocks. Felsic magmas are much more viscous than the intermediate magmas. Additionally, felsic magmas may have very high gas contents. In some igneous rocks and in most metamorphic rocks, microcline is the common potassium feldspar.
Microcline can accommodate only a little sodium and, like orthoclase, may occur with albite.
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