Cu5FeS4

Cu5FeS4, known as bornite, is a copper iron sulfide mineral and an important copper ore. It commonly occurs in hydrothermal veins and porphyry copper deposits, and is frequently found alongside chalcopyrite, pyrite, magnetite, and sphalerite. Bornite forms through sulfide mineralization processes in copper-rich environments and is widely distributed in copper-bearing ore districts around the world.

In hand specimen and on fresh surfaces, bornite displays a metallic luster and a characteristic copper-bronze color that tarnishes readily to iridescent blues, purples, and golds. It crystallizes in the isometric (cubic) system, but well-formed crystals are uncommon; the material is more typically granular, massive, or in irregular masses. The mineral lacks distinctive cleavage and has a hardness of about 3 on the Mohs scale. Its specific gravity is commonly around 5.0, reflecting its copper and iron content.

Occurrence and distribution: Bornite is found in many copper-producing regions worldwide, with notable occurrences in Chile, the United States, Peru, Canada, and Russia. It is often encountered in association with chalcopyrite, a primary copper ore, and forms part of the sulfide assemblages that constitute many porphyry copper systems and secondary supergene enrichment zones.

Etymology and history: The mineral was named in honor of the Austrian mineralogist Ignaz von Born (1742–1791). The name has been in use since the 18th century to distinguish this copper iron sulfide from other sulfide minerals.

Economic significance: Bornite serves as an ore of copper where it is sufficiently concentrated, contributing to copper production after processing and refining.