Cubanite
Cubanite
Copper iron sulfide mineral
Cubanite is a copper iron sulfide mineral that commonly occurs as a minor alteration mineral in magmatic sulfide deposits. It has the chemical formula CuFe2S3 and when found, it has a bronze to brass-yellow appearance. On the Mohs hardness scale, cubanite falls between 3.5 and 4 and has a orthorhombic crystal system.[2] Cubanite is chemically similar to chalcopyrite; however, it is the less common copper iron sulfide mineral due to crystallization requirements.
Cubanite occurs in high temperature hydrothermal mineral deposits with pyrrhotite and pentlandite as intergrowths with chalcopyrite.[4] It results from exsolution from chalcopyrite at temperatures below 200 to 210 °C.[4] If cubanite is exposed to temperatures above 210 °C, it will transform into isocubanite. After this transformation, if it begins to cool, it will not revert to cubanite.[5] Upon its transformation to isocubanite it will lose its highly magnetic property due to its change from an orthorhombic to a cubic crystal structure.[6] Cubanite has been identified on chondrites and within dust grain samples and has improved the precision of copper isotope analysis.