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:
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).
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).
At the Hilton mine, Scordale, Murton, Eden, Cumbria, England, UK, baryte
pseudomorphs after witherite have been found
(Minrec 41-1 Supplement p109).
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).
At Snailbeach mine, near Minsterley, Shropshire, England, UK, witherite occurs impregnated with hydrocarbon
and overgrown by baryte
(RES p271, 274).
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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