- Muscovite
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Muscovite
Muscovite with albite from Doce valley, Minas Gerais, Brazil (dimensions: 6×5.3×3.9 cm)General Category Silicate mineral Phyllosilicate Chemical formula KAl2(AlSi3O10)(F,OH)2 Strunz classification 09.EC.15 Dana classification 71.02.02a.01 Crystal symmetry 2/m – prismatic Unit cell a = 5.199 Å, b = 9.027 Å, c = 20.106 Å, β = 95.78°; Z = 4 Identification Color White, grey, silvery Crystal habit massive to platy Crystal system Monoclinic (2/m), space group C 2/m Twinning common on the [310] less common on the {001} Cleavage Perfect on the {001} Fracture Micaceous Tenacity Elastic Mohs scale hardness 2–2.5 parallel to {001}
4 right angle to {001}Luster Vitreous, silky, pearly Streak White Diaphaneity transparent to translucent Specific gravity 2.76–3 Optical properties Biaxial (-) Refractive index nα = 1.552–1.576
nβ = 1.582–1.615
nγ = 1.587–1.618Birefringence δ = 0.035 – 0.042 Pleochroism weak when colored Dispersion r > v weak Ultraviolet fluorescence None References [1][2][3] Muscovite (also known as common mica, isinglass, or potash mica[4]) is a phyllosilicate mineral of aluminium and potassium with formula KAl2(AlSi3O10)(F,OH)2, or (KF)2(Al2O3)3(SiO2)6(H2O). It has a highly-perfect basal cleavage yielding remarkably-thin laminæ (sheets) which are often highly elastic. Sheets of muscovite 5 metres by 3 metres have been found in Nellore, India.[5]
Muscovite 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. It is anisotropic and has high birefringence. Its crystal system is monoclinic. The green, chromium-rich variety is called fuchsite; mariposite is also a chromium-rich type of muscovite.
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.
References
- ^ Muscovite mineral information and data Mindat
- ^ Muscovite Mineral Data Webmineral
- ^ Handbook of Mineralgy
- ^ Encyclopædia Britannica
- ^ P. C. Rickwood (1981). "The largest crystals". American Mineralogist 66: 885–907. http://www.minsocam.org/ammin/AM66/AM66_885.pdf.
Serpentine group Clay mineral group Chlorite1 · Dickite · Halloysite · Illite · Ilmenite · Kaolinite · Montmorillonite · Nacrite · Nontronite · Palygorskite · Saponite · Sepiolite · Serpentine1 · TalcMica group Chlorite group 1. Serpentine and Chlorite are sometimes considered clay mineralsCategories:- Potassium minerals
- Aluminium minerals
- Mica group
- Monoclinic minerals
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