Norman and Gertrude Pendleton mineral collection Witherite Illinois — Photo: Cs california · CC BY-SA 3.0
Witherite
Barium carbonate — the aragonite-group mineral whose twins form distinctive pseudo-hexagonal shapes.
Intro adapted from Wikipedia (CC BY-SA).
Witherite is an IMA-recognized mineral species in the carbonate class, with the chemical formula Ba(CO₃).
It crystallizes in the orthorhombic crystal system (space group Pmcn). It is a member of the Aragonite structural group.
Key properties: Mohs hardness 3–3.5; specific gravity 4.22–4.31; typically colorless or white or gray or yellow or brown; White streak; Vitreous, resinous on fractures luster; refractive index 1.627; optically biaxial.
IMA symbol Wth, grandfathered status — known before the IMA’s founding, named in 1784.
Usually occurs in minor amounts in low-temperature hydrothermal veins, typically an alteration product of barite; may be of anoxic sedimentary origin, barium supplied by volcanic hot-spring activity; uncommon in coal measures.
It is found associated with Barite, fluorite, calcite, galena.
In honor of Dr. William Withering (1741–1799), English physician and mineralogist, who first noted the mineral.
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