Witherite

Witherite
Witherite from Alston Moor District, Cumbria, England
General
Category	Carbonate mineral
Formula (repeating unit)	BaCO3
IMA symbol	Wth[1]
Strunz classification	5.AB.15
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pmcn
Unit cell	a = 5.31 Å, b = 8.9 Å c = 6.43 Å; Z = 4
Identification
Color	Colorless, white, pale gray, with possible tints of pale-yellow, pale-brown, or pale-green
Crystal 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
Mohs scale hardness	3.0–3.5
Luster	Vitreous, resinous on fractures
Streak	White
Diaphaneity	Subtransparent to translucent
Specific gravity	4.3
Optical properties	Biaxial (−)
Refractive index	nα = 1.529 nβ = 1.676 nγ = 1.677
Birefringence	δ = 0.148
2V angle	Measured: 16°, calculated: 8°
Dispersion	Weak
Ultraviolet fluorescence	Fluorescent and phosphorescent, short UV=bluish white, long UV=bluish white
References	[2][3][4][5]

Witherite is a barium carbonate mineral, BaCO₃, in the aragonite group.^[2] Witherite crystallizes in the orthorhombic system and virtually always is twinned.^[2] 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.^[2] It fluoresces light blue under both long- and short-wave UV light, and is phosphorescent under short-wave UV light.^[2]

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,^[6] County Durham, England; Thunder Bay area, Ontario, Canada, Germany, and Poland (Tarnowskie Góry and Tajno at Suwałki Region).

Witherite was named after William Withering (1741–1799) an English physician and naturalist who in 1784 published his research on the new mineral. He could show that barite and the new mineral were two different minerals.^[4][7]