Witherite

From Wikipedia, the free encyclopedia
Witherite

Witherite from Cave-in-Rock (size: 4.9 x 3.7 x 3.2 cm)
General
Category Carbonate mineral
Formula
(repeating unit)		 BaCO3
Strunz classification 05.AB.15
Crystal symmetry Orthorhombic dipyramidal (2/m 2/m 2/m)
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.
Crystal system Orthorhombic
Twinning On {110}, universal
Cleavage Distinct on {010} poor on 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 [1][2][3]

Witherite is a barium carbonate mineral, BaCO3, in the aragonite group.[1] Witherite crystallizes in the orthorhombic system and virtually always is twinned.[1] 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.[1] It fluoresces light blue under both long- and short-wave UV light, and is phosphorescent under short-wave UV light.[1]

Two sharp pseudohexagonal crystals of witherite on calcite from Hardin County, Illinois (size: 6.4 x 5.4 x 3.4 cm)

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, USA; Settlingstones Mine Northumberland; Alston Moor, Cumbria; Anglezarke, Lancashire and Burnhope,[4] County Durham, England; Thunder Bay area, Ontario, Canada, Germany, and Poland (Tarnowskie Góry and Tajno at Suwałki Region).

Witherite was named for 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.[3][5]

Risk to human health

The 18th-century naturalist Dr. Leigh recorded its lethal effects after the death of a farmer's wife and child. James Watt Jnr. experimented with the mineral on animals and he recorded the same lethal properties.[6] Until the 18th century farmers at Anglezarke used the mineral as rat poison.[7]

Industrial use

An experiment conducted by Josiah Wedgwood, led to it being used in his 'Jasper ware'; the mineral had previously been considered as worthless.[7] Witherite has been used for hardening steel, and for making cement, glass, enamelware, soap, dye and explosives. [8]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Witherite mindat.org
  2. ↑ Handbook of Mineralogy
  3. ↑ 3.0 3.1 Webmineral data
  4. ↑ Ashburn, J.H., Mining Witherite in North-West Durham, Colliery Guardian, August 1963 (at Durham Mining Museum web-site)
  5. ↑ Withering, William (1784). "Experiments and Observations on Terra Poderosa". Philosophical Transactions of the Royal Society of London 74: 293–311. 
  6. ↑ Watt, James Jr. (1789). Memoirs and Proceedings of the Manchester Philosophical Society. p. 598. 
  7. ↑ 7.0 7.1 The Mining Magazine, March 1963, Vol 108, pages 133–139
  8. ↑ 'Looking Back' p10 Hexham Courant 10 January 2014 featuring a photograph of Settlingstones miners in 1905

External links

Media related to Witherite at Wikimedia Commons

This article is issued from Wikipedia. The text is available under the Creative Commons Attribution/Share Alike; additional terms may apply for the media files.