hemimorphite

n.
A usually white or colorless mineral, essentially Zn₄Si₂O₇(OH)₂·H₂O, an important ore of zinc. Also called calamine.

[HEMIMORPH(IC) + -ITE¹.]

A mineral sorosilicate having the composition Zn₄Si₂O₇(OH)₂.H₂O; an ore of zinc. Crystals are usually colorless and the aggregates white, but in some cases there are faint shades of green, yellow, and blue. The mineral has a vitreous luster, a hardness of 4½ to 5 on Mohs scale, and a specific gravity of 3.45.

Hemimorphite has a wide distribution and has been mined in Belgium, Germany, Romania, England, Algeria, and Mexico. In the United States it is found at Sterling Hill, New Jersey; Friedensville, Pennsylvania; and Elkhorn Mountains, Montana. See also Silicate minerals.

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Zn
Orthorhombic -- Rhombic pyramidal

Environment

The oxidized zone of zinc deposits.

Crystal description

Commonly crystallized in flattened prismatic plates up to an inch (2-3 cm) in length, attached at the base so that the unlike array of the lower end (indicative of its hemimorphism) is not apparent. Also in mammillary rounded groups with convexly crystallized surfaces (Franklin, New Jersey) and in smoother botryoidal knobs, granular, massive, and earthy.

Physical properties

White, sometimes slightly stained with iron or copper (brown and blue or green). Luster glassy; hardness 4Ɖ-5; specific gravity 3.4-3.5; fracture uneven to poor conchoidal; cleavage prismatic. Transparent to translucent. Strongly susceptible to electrical charges with changing temperature (pyroelectric); often fluorescent pale orange in longwave ultraviolet light.

Composition

Alkaline hydrated zinc silicate (67.5% ZnO, 25.0% SiO ₂ , 7.5% H ₂ O).

Tests

Decrepitates, and readily becomes frosted; develops a coating, yellow when hot, turning white when cold. Following roasting, fluoresces bright orange in longwave ultraviolet, white in shortwave ultraviolet.

Distinguishing characteristics

Distinguished from smithsonite by its lack of bubbling in acid; recognized as a zinc mineral by its colored coating after blowpiping. Heavier than prehnite, not found in basalts, and not associated with the similar zeolites.

Occurrence

No longer a significant American mineral. The best U.S. specimens were found in the Stone Mine, Leadville, Colorado, and at Elkhorn, Montana. Solid masses of white, giant crawling-caterpillar-like crystalline surfaces were obtained in the early days at Franklin, New Jersey. Excellent bladed examples now come from Mapimi, Durango, Mexico, with crystals 1 in. (2.5 cm) and more in length standing up in limonitic gossan pockets. Crusts of upstanding, flat, and well-terminated crystals Ɖ to 4 in. (1-7 cm) long and 蔹-ƈ in. (1-3 mm) broad, have likewise been found at Santa Eulalia, Chihuahua, Mexico, many smaller ones protruding like hedgehog spines from white dolomite rhombohedrons and more delicate than most hemimorphites. Any remaining crystals from the Joplin, Missouri, district are small, on cavernous ocher hemimorphite masses mixed with a brown and earthy smithsonite ("dry-bone ore").

Remarks

The old name, calamine, was once widely used but has been changed by international consent to hemimorphite, which describes the asymmetrical crystal class (no center of symmetry) to which it belongs. The current name eliminates centuries of confusion resulting from the European miner's use of "calamine" for both carbonate and silicate.

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The noun has one meaning:

Meaning #1: a white mineral; a common ore of zinc
  Synonym: calamine

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