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Muscovite

Muscovite

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While some minerals are responsible for the formation of either the igneous, metamorphic or sedimentary rocks, others like the muscovite can be found in all three. The name "Muscovite" originates from "Muscovy glass", which was its name because it was used as windows in Russia. Muscovite, also referred to as "isinglass" or "common mica", has the chemical formula KAl2 (Al,Si3 O10)(F,OH)2.

It is a stratified structure, consisting of sheets of aluminium silicate, which are bonded by a weak force of potassium ion layers. Muscovite is common mica and can be found in pegmatites, gneisses, schists and granites. The potassium ion strata are responsible for its ideal cleavage.

Although, muscovite is not regarded as a valuable mineral, it is associated with some minerals that are of value and exceptional beauty. Some of these minerals include topaz, almadino, beryl and tourmaline. Star Muscovite, a variety found in Brazil is yellow and resembles a five-pointed star. Fuchsite, a deep green diversity, obtains its colour from impurities of chrominum.

Other characteristics of Muscovite:

·    Muscovite can be coloured white, brown, silver or green.

·    It has a vitreous, pearly or silky lustre and a white streak.

·    The crystals are clear to translucent.

·    It has a monoclinic crystal arrangement.

·    The crystals of the muscovite are in tube form and terminate at a pinnacoid. The prism faces are four in number and shaped like books, sometimes forming a pseudo-hexagonal shaped crystal.

·    Its perfect cleavage produces thin flakes.

·    It has an uneven fracture which is not seen easily.

·    The sheets of the cleavage can bend and are resilient due to their flexibility and elasticity.

·    Muscovite can be found in Pakistan, Brazil, USA and India.

Since the muscovite sheets have excellent insulating characteristics, they are used to make electrical components and for fireproofing. They were also used as lubricants and as windows for ovens before the use of synthetic materials.

Additional Resources

Mineralogy   Nepheline   Onyx

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