What is Bornite?
Bornite is an important copper sulphide and a favourite collector mineral because its surface can develop intense iridescent colours. Fresh bornite is copper-red to brown before tarnishing.
Mineralogy and structure
Bornite has the formula Cu5FeS4. It is orthorhombic at ordinary conditions after ordering on cooling, while higher-temperature material can have higher symmetry. Hardness is about 3.
Colour and appearance
Fresh surfaces are copper red to pinchbeck brown and quickly develop purple, blue, green and gold tarnish. Massive and granular material is common; crystal forms are less frequent than colourful polished surfaces.
Formation and localities
Bornite occurs in hydrothermal copper deposits, skarns, porphyry systems and some sedimentary copper ores. It is associated with chalcopyrite, chalcocite, pyrite, quartz and calcite in localities worldwide.
Collecting and care
The term peacock ore should be used carefully because some commercial material is artificially treated. State whether the iridescence is natural, observed, or unknown, and protect soft surfaces from scratching.
Bornite and zodiac signs
Popular crystal pages often associate Bornite with Scorpio or Leo because of its copper colours and dramatic iridescence. These associations are not scientific.
Symbolic and esoteric associations
Esoteric traditions may use bornite as a symbol of change, colour and transformation. The metaphor can accompany a specimen description but does not establish a physical effect.
