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Muscovite
	; Muscovite from a pegmatite outcrop along the Patapsco River in Baltimore County, Maryland.
General
Category	Silicate mineral
Chemical formula	KAl2(AlSi3O10)(F,OH)2
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} to 4 right angle to {001}
Luster	Vitreous
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 = 1.587–1.618
Birefringence	δ = 0.035 - 0.042
Pleochroism	weak when colored
Dispersion	r > v weak
Ultraviolet fluorescence	None
References

For other uses, see Muscovite (disambiguation).

Muscovite (also known as Common mica, Isinglass, or Potash mica^[4]) is a phyllosilicate mineral of aluminium and potassium with formula K Al₂(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. 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 high birefringence. Its crystal system is monoclinic.

[edit] See also

[edit] 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.

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[0] Muscovite mineral information and data Mindat

[1] Muscovite Mineral Data Webmineral

[2] Handbook of Mineralgy

[3] Encyclopædia Britannica

[4] P. C. Rickwood (1981). "The largest crystals". American Mineralogist 66: 885-907. http://www.minsocam.org/ammin/AM66/AM66_885.pdf.

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