| 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]
- ^ 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.
- ^ a b c d e Witherite mindat.org
- ^ Handbook of Mineralogy
- ^ a b Webmineral data
- ^ Mineralienatlas
- ^ Ashburn, J.H., Mining Witherite in North-West Durham, Colliery Guardian, August 1963 (at Durham Mining Museum web-site)
- ^ 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.