muscovite

{{Infobox mineral | name = Muscovite | category = Phyllosilicate minerals | group = Mica group, dioctahedral mica group | image = Muscovite-Albite-122887.jpg | imagesize = | caption = Muscovite with albite from Doce valley, Minas Gerais, Brazil (dimensions: 6 × 5.3 × 3.9 cm) | formula = KAl2(AlSi3O10)(F,OH)2 | IMAsymbol = Ms | molweight = | strunz = 9.EC.15 | dana = 71.02.02a.01 | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = C2/c | unit cell = a = 5.199 Å, b = 9.027 Å, c = 20.106 Å, β = 95.78°; Z = 4 | color = White, grey, silvery | habit = Massive to platy | twinning = Common on the [310], less common on the {001} | cleavage = Perfect on the {001} | fracture = Micaceous | tenacity = Elastic | mohs = 2–2.5 parallel to {001} 4 right angle to {001} | luster = Vitreous, silky, pearly | polish = | refractive = nα = 1.552–1.576 nβ = 1.582–1.615 nγ = 1.587–1.618 | opticalprop = Biaxial (−) | birefringence = δ = 0.035 – 0.042 | dispersion = r > v weak | pleochroism = Weak when colored | fluorescence= None | absorption = | streak = White | gravity = 2.76–3 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent to translucent | other = | references = }}

Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated 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 laminae (sheets) which are often highly elastic. Sheets of muscovite have been found in Nellore, India.