Description
The mineral covellite or covelline is a copper sulfide with the chemical formula CuS. It may also contain some iron. This opaque, indigo-blue or darker mineral has a hexagonal crystal system, with edges a = 379.2 pm and c = 1634 pm (space group P63/mmc). The crystals are plate-shaped due to perfect cleavage along the [0001] crystal plane. The color is blue. The streak color is lead-gray and shiny. The structure of covelline is quite complex. One-third of the copper and sulfur atoms form a planar layer with a graphite structure (or more correctly: boron nitride). Two-thirds of the sulfur atoms form sulfur pairs S2, as also known from the pyrite structure—which are perpendicular to the planar layer with copper atoms between them. Covelline is a metallic conductor. Electronically, it is best described as Cu+3S-S22- with a delocalized gap in the valence band that is primarily sulfuric. The mineral is named after the Italian mineralogist Nicollo Covelli (1790–1829). Covellite consists of approximately 66.5% copper, making it a very valuable copper ore when found in large quantities. The remaining 33.5% is primarily sulfur.
