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ZnCO3
Hexagonal
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| Figure 23-13. Crystal drawing of smithsonite from Franklin. Drawing is from Palache (1935) who provided crystallographic data. | ||
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Smithsonite, a zinc carbonate mineral, was possibly first reported by Nuttall (1822) as carbonate of zinc, but he might have seen hydrozincite. Although reported from both Franklin and Sterling Hill, smithsonite is anomalously rare in these orebodies so rich in carbonate and zinc. This may be partially explained by the decarbonatization of pre-existing smithsonite to form zincite.
Palache (1928a, 1935) described and illustrated colorless, scalenohedral crystals of smithsonite (Figure 23-13), with a density of 4.43 g/cm3, and indices of refraction w = 1.85 and e = 1.625, but such crystals are rare. The preponderance of the very sparse local smithsonite is impure and massive. Palache (1935) reported earthy white films on zincite and an occurrence in a vein, but few observations of any kind have been made on verified material. No measurements have been made on analyzed material. Bostwick (1992) reported it to have a moderate white fluorescence in shortwave and longwave ultraviolet. There are no chemical data.
From Franklin, Palache reported fine crystals, white coatings on zincite, and a foot-thick vein he considered to be derived from sphalerite. It was reported and illustrated from the Buckwheat Dolomite (Peters et al., 1983); it should be emphasized that this occurrence of smithsonite is probably unrelated genetically to the orebody zinc minerals.
At Sterling Hill, Frondel (1972) reported the same coatings on zincite and also reported it as stalactitic masses, globular aggregates, and crusts. Some so-labeled specimens have proven to be hydrozincite (which would also give positive chemical tests for Zn and carbonate). Much of the light blue material and white, dull, earthy material from Sterling Hill which has been mislabeled smithsonite is in fact hemimorphite. The writer has found brown granular smithsonite as part of the impure yellow undercoating of Sterling Hill hemimorphite specimens. Much local calcite has been mislabeled as smithsonite.
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| Copyright © 1995 by Pete J. Dunn |
Website
by Herb Yeates
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Link
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This
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