Witherite

Witherite
Witherite from Alston Moor District, Cumbria, England
General
CategoryCarbonate mineral
Formula
(repeating unit)
BaCO3
IMA symbolWth[1]
Strunz classification5.AB.15
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPmcn
Unit cella = 5.31 Å, b = 8.9 Å
c = 6.43 Å; Z = 4
Identification
ColorColorless, white, pale gray, with possible tints of pale-yellow, pale-brown, or pale-green
Crystal habitStriated short prismatic crystals, also botryoidal to spherical, columnar fibrous, granular, massive.
TwinningOn {110}, universal
CleavageDistinct on {010} poor on {110}, {012}
FractureSubconchoidal
Mohs scale hardness3.0–3.5
LusterVitreous, resinous on fractures
StreakWhite
DiaphaneitySubtransparent to translucent
Specific gravity4.3
Optical propertiesBiaxial (−)
Refractive indexnα = 1.529 nβ = 1.676 nγ = 1.677
Birefringenceδ = 0.148
2V angleMeasured: 16°, calculated: 8°
DispersionWeak
Ultraviolet fluorescenceFluorescent 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]

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c d e Witherite mindat.org
  3. ^ Handbook of Mineralogy
  4. ^ a b Webmineral data
  5. ^ Mineralienatlas
  6. ^ Ashburn, J.H., Mining Witherite in North-West Durham, Colliery Guardian, August 1963 (at Durham Mining Museum web-site)
  7. ^ Withering, William (1784). "Experiments and Observations on Terra Poderosa". Philosophical Transactions of the Royal Society of London. 74: 293–311. doi:10.1098/rstl.1784.0024. S2CID 186210361.