BORNITE

Cu₅FeS₄
Cubic

Bornite, a copper iron sulfide mineral, was first reported from Franklin by Palache (1928a) and from Sterling Hill by Frondel (1972); it does not occur in economic quantities locally. It has been found sparingly in the marble quarries. Bornite elsewhere has been called peacock ore in allusion to the surficial violetish tarnish it quickly obtains on exposure. However, the local and specialized use of this term is almost wholly restricted to the description of iridescent franklinite. Bornite is opaque, moderately brittle, and orange-pink on freshly broken surfaces. There have been no published analytical studies since the data given by Palache (1928, 1935). Several unpublished analyses by the writer show Franklin bornite to have nearly ideal composition.

At Franklin, bornite occurs in masses up to 10 cm with sphalerite, chalcopyrite, galena, and sparse carrollite. The assemblages have not been studied in detail. At Sterling Hill, bornite has been found with calcite, franklinite, and willemite, and with arsenopyrite, calcite and franklinite, the latter assemblage from the 1680 level. It has also been found associated with loellingite, arsenopyrite, magnetite, galena, chalcopyrite, and sphalerite from the 1340 pillar, slightly above the 1300 level, and was reported from below the 700 level by Jenkins and Misiur (1994).

Mislabeled specimens are common, due in large part to the occasional iridescent tarnishes of franklinite, chalcopyrite, and chalcocite, which in some cases mimic that of bornite. The orange-pink color of a freshly broken surface aids in identification.

Copyright © 1995 by Pete J. Dunn			Website by Herb Yeates
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This page created: January 11, 2001