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The Mineral Muscovite (Mica)
muscovite mineral picture

muscovite picture

Muscovite is more commonly known by its common name Mica, Potash Mica or Isinglass. This mineral has a formula KAl2(AlSi3O10)(F,OH)2.  This mineral represents a phyllosilicate configuration of Potassium and Aluminum.  Sometimes this mineral is also accorded the formula KF)2(Al2O3)3(SiO2)6(H2O. This material’s basal cleavage  yields very thin and elastic sheets or Lamine.  Nellore in India has been a producer of 5 meter X 3 meter muscovite sheets.    

Chemical Formula  
KAl2(AlSi3O10)(F,OH)2

Derivation of Name  
Muscovite gets its name from Muscovy-glass, a name given to the mineral in Elizabethan England because of its use in medieval Russia as a cheaper substitute for glass in windows. This practice became extensively known in England during the 16th century when it was first mentioned during 1568  in letters by George Turberville, the secretary of England's ambassador to the Russian tsar Ivan the Terrible.

Occurrence         
Muscovite is the most widespread mica, located in granites, gneisses, pegmatites and schists, and also as a secondary mineral or a contact metamorphic rock or as a result of the modification of Feldspar, Topaz, Kyanite, etc. In pegmatites, it is regularly found as huge sheets that are valued commercially. Muscovite is required for manufacturing of insulating and fireproofing materials and somewhat as a lubricant.            

Gemology  
It is not used as gemstones.

Source 
Mainly found in India, Brazil, Pakistan and USA.

Mineralogy  
An extensively spread mineral that forms rocks, Muscovite is found in detrital sedimentary, rocks and igneous, metamorphic rocks. Comprised of sheets lightly bonded by Potassium ions, Muscovite displays flawless cleavage, despite which   these sheets feature high durability.  You normally find them in the sands that have undergone excessive erosion followed by transportation other minerals are not able to withstand. 

 Since muscovite sheets possess strong insulating properties against soaring heat and high electricity, they are used for producing numerous electrical components including insulations. They were hitherto utilized in kitchen windows before synthetic materials replaced them.

It can be colorless or have tints of gray, brown, green, yellow, or (infrequently) red or violet, and can be translucent or transparent. It is anisotropic and has high birefringence (optically anisotropic). It has a monoclinic crystal system.

Density     
2.76 to 3.00

Mohs hardness
2–2.25 parallel to the [001] face but 4 when perpendicular to [001]

     
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