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SiO2
Hexagonal
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| Figure 19-1. Crystal drawing of quartz from Franklin. Drawing is from Palache (1935) who provided crystallographic data. | ||
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Quartz, a silicon dioxide mineral, is uncommon at both Franklin and Sterling Hill. It was originally noted by Vanuxem and Keating (1822b), and crystals were described by Palache (1928a, 1935). Although found abundantly in the microcline pegmatites which cut the orebody at Franklin and occurring in moderate amounts in the local rocks, especially in the gneisses, quartz is generally quite rare in the orebodies, even in silicate assemblages which are devoid of ore.
Crystals, to the extent known, are of common habit, except those figured by Palache (1928a, 1935). Frondel (1972) and Palache (1935) discussed the cryptocrystalline varieties, which are of trivial significance. Quartz is generally white to colorless, but may be stained by impurities; to cite one example, an apparent gray-blue color is caused by inclusions of magnesioriebeckite. Quartz has a vitreous luster, conchoidal fracture, and a density of 2.65 g/cm3. Large masses up to 30 cm are known but rare.
The best quartz specimens are of the prismatic, elongate, twisted crystals described by Palache (1935) as occurring with hematite and magnesioriebeckite (Figure 19-1). Superb, prismatic quartz crystals are also found in this assemblage. Equant, 1 cm crystals have been found associated with a chevron-like intergrowth of garnet and calcite and separately with talc, both from Franklin. Fine crystals were reported and illustrated from vugs in the Buckwheat Dolomite by Peters et al. (1983); some crystals are up to 2.5 cm in length, but most are small. Massive material is found associated with the notable bannisterite assemblage. Quartz occurs less commonly with massive rhodonite. Additionally, it is found as druses in vugs and veinlets and in sulfide assemblages at Sterling Hill (Jenkins and Misiur, 1994), and it is found as chert segregations up to 20 cm thick in the Kittatinny Limestone.
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| Copyright © 1995 by Pete J. Dunn |
Website
by Herb Yeates
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This
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