Home > American Minerals V – October 1 > MS1662 Chalcocite on Bornite (Butte)

Chalcocite on Bornite (Butte) - Sold

Chalcocite is a seemingly simple copper sulfide with nominal formula Cu2S. The simple formula belies the complexity of the mineral, whose unit cell contains 96 Cu atoms and 48 S atoms (Evans, 1979). The name chalcocite derives from the Greek chalco for copper. This specimen consists of chalcocite nucleated on bornite crystals. Haidinger (1845) named the mineral after Ignatius von Born (1742-1791), an eminent mineralogist of his time. Like chalcocite, bornite is especially complex structurally, and its cubic morphology hides the complex arrangement of Cu and Fe atoms in the mineral (Ding et al., 2005).

This is a peculiar intergrowth of chalcocite and bornite. According to Jenkins & Lorengo (2002), such intergowths are locally known as "chalcoborn." The iridescent blue globules reach 1 cm on this example, and cover one side of the specimen. Minor pyrite is also associated. This specimen was part of the Charles Trantham (1936-2020) estate.