Muscovite
| Muscovite | |
|---|---|
 Muscovite with albite from Doce valley, Minas Gerais, Brazil (dimensions: 6×5.3×3.9 cm) | |
| General | |
| Category | Phyllosilicate |
Formula .mw-parser-output .noboldfont-weight:normal (repeating unit) | KAl2(AlSi3O10)(F,OH)2 |
| Strunz classification | 9.EC.15 |
| Dana classification | 71.02.02a.01 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | C2/c |
| 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 |
| 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 = 1.587–1.618 |
| Birefringence | δ = 0.035 – 0.042 |
| Pleochroism | Weak when colored |
| Dispersion | r > v weak |
Ultraviolet fluorescence | None |
| References | [1][2][3][4] |
Muscovite (also known as common mica, isinglass, or potash mica[5]) is a hydrated phyllosilicate mineral of aluminium and potassium with formula KAl2(AlSi3O10)(FOH)2, or (KF)2(Al2O3)3(SiO2)6(H2O). It has a highly perfect basal cleavage yielding remarkably thin laminae (sheets) which are often highly elastic. Sheets of muscovite 5 meters × 3 meters (16.5 feet × 10 feet) have been found in Nellore, India.[6]
Muscovite with beryl (var. morganite) from Paprok, Afghanistan
Muscovite (var. alurgite), from Prabornaz Mine, Aosta Valley, Italy
Tabular muscovite crystals in a gneiss in thin section viewed under cross-polarized light at 2x magnification.
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 muscovite comes from Muscovy-glass, a name given to the mineral in Elizabethan England due to its use in medieval Russia as a cheaper alternative to glass in windows. This usage became widely known in England during the sixteenth century with its first mention appearing in letters by George Turberville, the secretary of England's ambassador to the Russian tsar Ivan the Terrible, in 1568.
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| Small specimen of Muscovite (fuchsite) from Brazil. |
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References
^ Mineralienatlas
^ Muscovite mineral information and data Mindat
^ Muscovite Mineral Data Webmineral
^ Handbook of Mineralogy
^ Encyclopædia Britannica
^ P. C. Rickwood (1981). "The largest crystals" (PDF). American Mineralogist. 66: 885–907..mw-parser-output cite.citationfont-style:inherit.mw-parser-output .citation qquotes:"""""""'""'".mw-parser-output .citation .cs1-lock-free abackground:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration abackground:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center.mw-parser-output .citation .cs1-lock-subscription abackground:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registrationcolor:#555.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration spanborder-bottom:1px dotted;cursor:help.mw-parser-output .cs1-ws-icon abackground:url("//upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Wikisource-logo.svg/12px-Wikisource-logo.svg.png")no-repeat;background-position:right .1em center.mw-parser-output code.cs1-codecolor:inherit;background:inherit;border:inherit;padding:inherit.mw-parser-output .cs1-hidden-errordisplay:none;font-size:100%.mw-parser-output .cs1-visible-errorfont-size:100%.mw-parser-output .cs1-maintdisplay:none;color:#33aa33;margin-left:0.3em.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-formatfont-size:95%.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-leftpadding-left:0.2em.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-rightpadding-right:0.2em
External links
Media related to Muscovite at Wikimedia Commons
Media related to Muscovite at Wikimedia Commons
