witherite

{{infobox mineral | name = Witherite | category = Carbonate mineral | image = File:Witherite-48305.jpg | caption = Witherite from Alston Moor District, Cumbria, England | formula = BaCO3 | IMAsymbol = Wth | molweight = | strunz = 5.AB.15 | dana = | system = Orthorhombic | class = Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) | symmetry = Pmcn | unit cell = a = 5.31 Å, b = 8.9 Å c = 6.43 Å; Z = 4 | color = Colorless, white, pale gray, with possible tints of pale-yellow, pale-brown, or pale-green | colour = | habit = Striated short prismatic crystals, also botryoidal to spherical, columnar fibrous, granular, massive. | twinning = On {110}, universal | cleavage = Distinct on {010} poor on {110}, {012} | fracture = Subconchoidal | tenacity = | mohs = 3.0–3.5 | luster = Vitreous, resinous on fractures | streak = White | diaphaneity = Subtransparent to translucent | gravity = 4.3 | density = | polish = | opticalprop = Biaxial (−) | refractive = nα = 1.529 nβ = 1.676 nγ = 1.677 | birefringence = δ = 0.148 | pleochroism = | 2V = Measured: 16°, calculated: 8° | dispersion = Weak | extinction = | length fast/slow = | fluorescence = Fluorescent and phosphorescent, short UV=bluish white, long UV=bluish white | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | references = }} Witherite is a barium carbonate mineral, BaCO3, in the aragonite group. Witherite crystallizes in the orthorhombic system and virtually always is twinned. The mineral is colorless, milky-white, grey, pale-yellow, green, to pale-brown. The specific gravity is 4.3, which is high for a translucent mineral. It fluoresces light blue under both long- and short-wave UV light, and is phosphorescent under short-wave UV light.

Witherite forms in low-temperature hydrothermal environments. It is commonly associated with fluorite, celestine, galena, barite, calcite, and aragonite. Witherite occurrences include: Cave-in-Rock, Illinois, US; Pigeon Roost Mine, Glenwood, Arkansas, US; Settlingstones Mine Northumberland; Alston Moor, Cumbria; Anglezarke, Lancashire and Burnhope, County Durham, England; Thunder Bay area, Ontario, Canada, Germany, and Poland (Tarnowskie Góry and Tajno at Suwałki Region).