Witherite


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.
Witherite was named after William Withering 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.

Discovery

In 1789 the eminent German geologist Abraham Gottlob Werner named the mineral witherite in honour of William Withering. The Matthew Boulton mineral collection of Birmingham Museum and Art Gallery may contain one of the earliest known specimens of witherite. A label in Boulton's handwriting, records: "No.2 Terra Ponderosa Aerata, given me by Dr. Withering”.

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. Until the 18th century farmers at Anglezarke used the mineral as rat poison.

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.
Witherite has been used for hardening steel, and for making cement, glass, enamelware, soap, dye and explosives.