Cubanite
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. Cubanite is chemically similar to chalcopyrite; however, it is the less common copper iron sulfide mineral due to crystallization requirements.
| Cubanite | |
|---|---|
Striated, cyclically-twinned cubanite crystals from the Chibougamau mines of Quebec (size: 1.5 × 1.3 × 1.0 cm) | |
| General | |
| Category | Sulfide mineral |
| Formula (repeating unit) | CuFe2S3 |
| IMA symbol | Cbn |
| Strunz classification | 2.CB.55a |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Space group | Pcmn |
| Unit cell | a = 6.467(1) Å, b = 11.117(1) Å, c = 6.231(2) Å; Z = 4 |
| Identification | |
| Color | Bronze to brass-yellow |
| Crystal habit | Crystals elongated to thick tabular, striated also massive |
| Twinning | Common with twin plane {110} in pairs, also as fourlings and pseudohexagonal sixlings |
| Cleavage | Parting on {110} and {130} |
| Fracture | Conchoidal |
| Mohs scale hardness | 3.5–4 |
| Luster | Metallic |
| Streak | Black |
| Diaphaneity | Opaque |
| Specific gravity | 4.0–4.2 |
| Optical properties | Distinctly anisotropic on polished surface |
| Other characteristics | Strongly magnetic |
| References | |
Cubanite occurs in high temperature hydrothermal mineral deposits with pyrrhotite and pentlandite as intergrowths with chalcopyrite. It results from exsolution from chalcopyrite at temperatures below 200 to 210 °C. 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. Upon its transformation to isocubanite it will lose its highly magnetic property due to its change from an orthorhombic to a cubic crystal structure. Cubanite has been identified on chondrites and within dust grain samples and has improved the precision of copper isotope analysis.