Witherite

witherite

barytocalcite

alstonite

baryte

Images

Formula: Ba(CO3)
Anhydrous normal carbonate, barium mineral, aragonite group. Witherite is epitaxial on barytocalcite and baryte is epitaxial on witherite (Mindat)
Crystal System: Orthorhombic
Specific gravity: 4.289 to 4.293 measured, 4.26 calculated
Hardness: 3 to 3½
Streak: white
Colour: colourless, white, pale yellow; colourless in transmitted light
Solubility: Readily soluble in hydrochloric acid; moderately soluble in sulphuric and nitric acids
Common impurities: Ca, Sr
Environments:

Hydrothermal environments

Witherite occurs typically, along with baryte and other barium-bearing minerals, in epithermal (low temperature) hydrothermal mineral veins, usually resulting from the alteration of baryte (HOM). Other commonly associated minerals include calcite, alstonite, sphalerite and galena.

Localities

At the type locality, the Brownley Hill Mine, Nenthead, Alston Moor, Eden, Cumbria, England, UK, witherite is associated with alstonite, calcite, hydromagnesite, galena, pyrite and marcasite (Minrec 31.3.248).
Witherite from Brownley Hill - Image

At Rampgill Mine, Nenthead, Alston Moor, Eden, Cumbria, England, UK, witherite occurs with calcite and fluorite, all of which fluoresce under short wave UV, witherite bright yellow, calcite pink and fluorite deep lilac-blue (AESS).
Witherite from Rampgill - Image

At the Scaleburn Mine, Nenthead, Alston Moor, Eden, Cumbria, England, UK, witherite occurs with baryte. The witherite fluoresces yellow-white under short wave UV (AESS).
Witherite from the Scaleburn Mine - Image

At the Nentsberry Haggs mine, Alston Moor, Eden, Cumbria, England, UK, witherite is often encrusted with baryte and/or calcite, sometimes associated with altered alstonite (JRS 17.47-48). Witherite has also been found on galena and dolomite, sometimes partly altered to baryte (SY p174).
Witherite from Nentsberry Haggs - Image

At the Hilton mine, Scordale, Murton, Eden, Cumbria, England, UK, baryte pseudomorphs after witherite have been found (Minrec 41-1 Supplement p109).
Witherite from the Hilton Mine - Image

At the Fallowfield Mine, Acomb, Northumberland, England, UK, fine specimens of witherite are found, often coated with a dusting of baryte and occasionally found intergrown with alstonite (Minrec 41-1 Supplement p102, SY p174).
Witherite from Fallowfield - Image

At Snailbeach mine, near Minsterley, Shropshire, England, UK, witherite occurs impregnated with hydrocarbon and overgrown by baryte (RES p271, 274).
Witherite from Snailbeach - Image

Ay the Glacier National Park, Glacier county, Montana, USA, considerable witherite has been observed filling cavities in the Altyn limestone. This limestone is a highly siliceous calcium-magnesium-carbonate rock containing rounded to angular quartz and feldspar grains.
The witherite appears:
(1) in flat masses one to six inches in thickness parallel to the bedding;
(2) in thin lenses one to three inches thick and six to eighteen inches across;
(3) in very irregular lumps up to two feet in diameter.
The witherite fills the cavities in pure translucent masses which are not associated with other minerals. The masses are colourless to pale buff and interlock in brush and fan shaped growths which extend from the walls of the openings towards the centres so as to nearly fill them (AM 9.154).

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