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Muscovite
From Wikipedia, the free encyclopedia
| Muscovite | |
|---|---|
 |
|
| General | |
| Category | Mineral Species |
| Chemical formula | KAl2(AlSi3O10)(F,OH)2 |
| Identification | |
| Molecular Weight | 398.71 gm |
| Color | White, grey, silvery |
| Crystal habit | massive to platy Crystaline |
| Crystal system | Monoclinic - Prismatic |
| Twinning | common on the [310] less common on the {001} |
| Cleavage | Perfect on the {001} |
| Fracture | Micaeous |
| Tenacity | Elastic |
| Mohs Scale hardness | 2-2.5, 4 |
| Luster | Vitreous |
| Refractive index | nα = 1.552 - 1.576 nβ = 1.582 - 1.615 nγ = 1.587 - 1.618 |
| Optical Properties | Biaxial |
| Birefringence | δ = 0.035 - 0.042 |
| Dispersion | r > v weak |
| Pleochroism | weak when colored |
| Ultraviolet fluorescence | None |
| Streak | White |
| Specific gravity | 2.76 - 3 |
| Density | 2.83 g/cm3 |
| Melting point | approximately 1320°C |
| Diaphaneity | transparent or translucent |
| References | [1][2] |
Muscovite (also known as Common mica, Isinglass, or Potash mica[3]) is a phyllosilicate mineral of aluminium and potassium with formula: KAl2(AlSi3O10)(F,OH)2. It has a highly perfect basal cleavage yielding remarkably thin laminae (sheets), which are often highly elastic. Sheets of muscovite 5 metres by 3 metres have been found in Nellore, India.[4]
Muscovite melts at approximately 1320°C, has a Mohs hardness of 2 - 2.25 parallel to the [001] face, 4 perpendicular to the [001] and a specific gravity of 2.76 - 3. It can be colorless or tinted through grays, browns, greens, yellows, or (rarely) violet or red, and can be transparent or translucent. The green chromium rich variety is called fuchsite.
Muscovite is the most common mica, found in granites, pegmatites, gneisses and schists, and as a contact metamorphic rock or as a secondary mineral resulting from the alteration of topaz, feldspar, kyanite, etc. In pegmatites, it is often found in immense sheets that are commercially valuable. Muscovite is in demand for the manufacture of fireproofing and insulating materials and to some extent as a lubricant.
The name of muscovite comes from Muscovy-glass, a name formerly used for the mineral because of its use in Russia for windows. It is anisotropic, and has quite a high birefringence. Its crystal system is monoclinic.
- ^ http://www.mindat.org/min-2815.html
- ^ http://www.webmineral.com/data/Muscovite.shtml
- ^ Encyclopædia Britannica
- ^ The Complete Encyclopedia of Minerals by P. Korbel and M. Novak
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