witherite

[German Witherit, after William Withering (1741-1799), British physician.]

The mineral form of barium carbonate. Witherite has orthorhombic symmetry and the aragonite structure type. Crystals, often twinned, may appear hexagonal in outline. It may be white or gray with yellow, brown, or green tints. Its hardness is 3.5 and its specific gravity 4.3.

Witherite may be found in veins with barite and galena. It is found in many places in Europe, and large crystals occur at Rosiclare, Illinois. See also Barium; Carbonate minerals; Hardness scales.

Environment

Low-temperature lead and fluorite ore veins.

Though orthorhombic, witherite twinned into pseudohexagonal trillings, most often resembling hexagonal bipyramids. Also in crusts with rounded surfaces; columnar and granular.

White, light yellowish, or gray. Luster glassy; hardness 3-3Ɖ; specific gravity 4.3-4.7; fracture uneven; cleavage 1 good and 2 poor. Brittle; translucent; commonly fluorescent blue.

Barium carbonate (77.7% BaO, 22.3% CO ₂ ); may contain some Ca.

Dissolves readily in hydrochloric acid with effervescence. Slender white needles form as 2:3 hydrochloric acid solution cools, and dissolve again on heating or dilution. Even dilute solutions form precipitate of barium sulfate crystals when sulfuric acid is added. A strong hydrochloric acid solution on a platinum wire placed in the flame gives a yellow-green flash (barium flame).

Recognized as a carbonate by its hardness and effervescence in acid. Recognized as witherite by the flame coloration and greater-than-average "heft."

Witherite is a surprisingly rare mineral and in its best occurrences accompanies lead ore (galena) in veins. The best specimens, 1-in. (to 3 cm) white pseudobipyramids, have always come from Cumberland and Northumberland, England. Comparable though generally smaller individual trillings, some of a stubbier habit, occur in the s. Illinois fluorite mines. Otherwise it appears to be very rare in the U.S., having been reported only in massive specimens near Yosemite National Park (associated with barite and some rare barium minerals) and at Thunder Bay, Ontario. Possibly it is more common than generally supposed because it is usually not recognized.

Its rarity can be accounted for in part by the ease with which it can be altered to the very insoluble sulfate, barite. When commonly associated sulfide minerals alter they produce excess sulfuric acid, which would immediately react with the soluble witherite, reprecipitating it as barite. However, at the Illinois locality, where fluorite is dominant, corroded barite suggests that some of the witherite appears still to be forming at the expense of the calcite rather than forming as barite.

Witherite from England

Witherite from England

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 non-metallic mineral. It fluoresces light blue under both long and short-wave UV and is phosphorescent under short-wave UV light.^[2]

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; Alston Moor, Anglezarke, Cumberland and Durham, England; Thunder Bay area, Ontario, Canada and Germany.

Witherite was named for William Withering (1741-1799) an English physician and naturalist.^[3]

See also

• List of minerals
• List of minerals named after people

References

1. ^ ^{a b} Witherite mindat.org
2. ^ The Mineral Witherite Mineral Galleries
3. ^ General Witherite Information Webmineral.com

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