langite

{{Infobox mineral | name = Langite | category = Copper minerals | boxwidth = 24 | boxbgcolor = | image = Langite-120989.jpg | imagesize = 260px | caption = Langite from Podlipa and Reinera Mines, Slovakia | formula = Cu4(SO4)(OH)6·2H2O | IMAsymbol = Lgt | molweight = 488.32 g/mol | strunz = 7.DD.10 | dana = 31.4.3.1 | system = Monoclinic | class = Domatic (m) (same H-M symbol) | symmetry = Pc | unit cell = a = 7.118, b = 6.031 c = 11.209 [Å] β = 90.00–90.02°; Z = 2 | color = Greenish blue, sky-blue to bluish green | habit = Crystals scaly, or as crusts; earthy | twinning = Common on {110}, typically repeated | cleavage = {001} perfect, {010} distinct | fracture = Uneven | tenacity = | mohs = 2.5 to 3 | luster = Vitreous, crusts silky | refractive = nα = 1.708 nβ = 1.760 nγ = 1.798 | opticalprop = Biaxial (−) r>v weak | birefringence = δ = 0.090 | pleochroism = X = c = light yellowish greenY = b = blue-greenZ = a = sky blue | streak = Blue green | gravity = 3.28 3.48 to 3.5 3.5 2.28 to 3.34 | density = | melt = | fusibility = | diagnostic = | solubility = Insoluble in water, easily soluble in dilute acids or NH4OH | diaphaneity = Translucent | other = May be altered to brochantite. Not radioactive | references = }}

Langite is a rare hydrated copper sulfate mineral, with hydroxyl, found almost exclusively in druses of small crystals. It is formed from the oxidation of copper sulfides, and was first described in specimens from Cornwall, United Kingdom. It is dimorphous with wroewolfeite. Langite was discovered in 1864 and named after the physicist and crystallographer Viktor von Lang (1838–1921), who was Professor of Physics at the University of Vienna, Austria.