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.
Several unpublished analyses by the writer show Franklin bornite to have nearly ideal composition.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. 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.