Chalcopyrite is a brassy-colored, copper iron sulfide. It was named by Johann Friedrich Henckel in 1725, from the Greek “chalkos” meaning copper, and “pyrites” meaning to strike fire. It has a green-black streak, yet tarnishes in a variety of iridescent purple, blue, and red. It sometimes goes by the term “peacock rock”. It is often mistaken for pyrite, but is a softer 3.5-4 on the Mohs scale. It is brittle, and can shatter if struck. It has poor cleavage, and fractures unevenly. It can be found in tetragonal crystal form, massive, and even botryoidal.
This mineral has been mined as a copper ore for thousands of years. Copper mixed with zinc creates brass, but mixed with tin creates bronze – a metal used in tools for ages. It is very common in sulfide veins, high-temperature hydrothermal veins, igneous dikes, and more. When oxidized, or weathered, chalcopyrite may form malachite, azurite, cuprite, and other minerals.
Group: Sulfide. The chemical formula is CuFeS2.
Klein, Cornelis and Cornelius S. Hurlbut, Jr., Manual of Mineralogy, Wiley, 20th ed., 1985, pp. 277 – 278