1911 Encyclopædia Britannica/Calamine
|←Calaïs and Zetes||1911 Encyclopædia Britannica, Volume 4
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CALAMINE, a mineral species consisting of zinc carbonate, ZnCO3, and forming an important ore of zinc. It is rhombohedral in crystallization and isomorphous with calcite and chalybite. Distinct crystals are somewhat rare; they have the form of the primitive rhombohedron (rr′ = 72° 20′), the faces of which are generally curved and rough. Botryoidal and stalactitic masses are more common, or again the mineral may be compact and granular or loose and earthy. As in the other rhombohedral carbonates, the crystals possess perfect cleavages parallel to the faces of the rhombohedron. The hardness is 5; specific gravity, 4.4. The colour of the pure mineral is white; more often it is brownish, sometimes green or blue: a bright-yellow variety containing cadmium has been found in Arkansas, and is known locally as "turkey-fat ore." The pure material contains 52% of zinc, but this is often partly replaced isomorphously by small amounts of iron and manganese, traces of calcium and magnesium, and sometimes by copper or cadmium.
Calamine is found in beds and veins in limestone rocks, and is often associated with galena and blende. It is a product of alteration of blende, having been formed from this by the action of carbonated waters; or in many cases the zinc sulphide may have been first oxidized to sulphate, which in solution acted on the surrounding limestone, producing zinc carbonate. The latter mode of origin is suggested by the frequent occurrence of calamine pseudomorphous after calcite, that is, having the form of calcite crystals. Deposits of calamine have been extensively mined in the limestones of the Mendip Hills, in Derbyshire, and at Alston Moor in Cumberland. It also occurs in large amount in the province of Santander in Spain, in Missouri, and at several other places where zinc ores are mined. The best crystals of the mineral were found many years ago at Chessy near Lyons; these are rhombohedra of a fine apple-green colour. A translucent botryoidal calamine banded with blue and green is found at Laurion in Greece, and has sometimes been cut and polished for small ornaments such as brooches.
The name calamine (German, Galmei), from lapis calaminaris, a Latin corruption of cadmia (καδμία), the old name for zinc ores in general (G. Agricola in 1546 derived it from the Latin calamus, a reed), was early used indiscriminately for the carbonate and the hydrous silicate of zinc, and even now both species are included by miners under the same term. The two minerals often closely resemble each other in appearance, and can usually only be distinguished by chemical analysis; they were first so distinguished by James Smithson in 1803. F.S. Beudant in 1832 restricted the name calamine to the hydrous silicate and proposed the name "smithsonite" for the carbonate, and these meanings of the terms are now adopted by Dana and many other mineralogists. Unfortunately, however, in England (following Brooke and Miller, 1852) these designations have been reversed, calamine being used for the carbonate and smithsonite for the silicate. This unfortunate confusion is somewhat lessened by the use of the terms zinc-spar and hemimorphite (q.v.) for the carbonate and silicate respectively.
- (L. J. S.)