Muscovite


Muscovite
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 = 1.587–1.618
Birefringence 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 with beryl (var. morganite) from Paprok, Afghanistan (dimensions: 5.9×4.8×3.4 cm)

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


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Look at other dictionaries:

  • Muscovite — Catégorie IX : silicates[1] Muscovite; sud est de Minas Gerais, Brésil …   Wikipédia en Français

  • muscovite — ● muscovite nom féminin (anglais Muscovy, Moscovie) Variété de mica blanc qui est un silicate hydraté naturel d aluminium et de potassium, que l on rencontre dans les granites et les micaschistes. (Elle est utilisée industriellement comme isolant …   Encyclopédie Universelle

  • Muscovite — ► NOUN 1) a native or citizen of Moscow. 2) (muscovite) a silver grey form of mica. ► ADJECTIVE ▪ relating to Moscow …   English terms dictionary

  • Muscovite — Mus co*vite, n. [See {Muscovy glass}.] 1. A native or inhabitant of Muscovy or ancient Russia; hence, a Russian. [1913 Webster] 2. An inhabitant of Moscow. [PJC] 3. (Min.) Common potash mica, essentially {KAl3Si3O10(OH)2}. It is used as an… …   The Collaborative International Dictionary of English

  • Muscovite — [mus′kə vīt΄] n. 1. a) a person born or living in Muscovy b) a Russian 2. a person born or living in Moscow adj. 1. a) of Muscovy b) Russian …   English World dictionary

  • muscovite — [mus′kə vīt΄] n. [formerly called Muscovy glass: see ITE1] a very common, light colored, soft mica, hydrous potassium aluminum silicate, KAl2 (AlSi3)O10 (OH) 2, used as an electrical or thermal insulator …   English World dictionary

  • Muscovite — /mus keuh vuyt /, n. 1. a native or inhabitant of Moscow. 2. a native or inhabitant of the Grand Duchy of Muscovy. 3. (l.c.) Mineral. common light colored mica, essentially KAl3Si3O10(OH)2, used as an electrical insulator. 4. Archaic. a Russian.… …   Universalium

  • Muscovite — UK [ˈmʌskəvaɪt] / US [ˈmʌskəˌvaɪt] noun [countable] Word forms Muscovite : singular Muscovite plural Muscovites someone from Moscow Derived word: Muscovite UK / US adjective …   English dictionary

  • muscovite — Mica Mi ca, n. [L. mica crumb, grain, particle; cf. F. mica.] (Min.) The name of a group of minerals characterized by highly perfect cleavage, so that they readily separate into very thin leaves, more or less elastic. They differ widely in… …   The Collaborative International Dictionary of English

  • muscovite — noun Etymology: Medieval Latin or New Latin Muscovia, Moscovia Moscow Date: 1535 1. capitalized a. a native or resident of the ancient principality of Moscow or of the city of Moscow b. Russian 2. [muscovy (glass)] a colorless to pale brown form… …   New Collegiate Dictionary