Chalcopyrite
From cornish semiconductor corporation
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- Lustre:Metallic
- Transparency:Opaque
- Colour:Brass yellow, often with an iridescent tarnish.
- Streak:Greenish black
- Hardness:3½ - 4 on Mohs scale
- Tenacity:Brittle
- Cleavage:Poor/Indistinct Indistinct on {011}, sometimes distinct.
- Fracture:Irregular/Uneven
Chalcopyrite is the main ore of copper, is softer than pyrite and fairly easy to find in usable quantities. It's rarely well crystallised, but forms thick veins and large blobs, usually in quartz.
Due to the copper content it has a very low overall resistance, I find it one of the easiest minerals to find good semiconducting junctions, it doesn't seem to alter much with oxidisation or weathering. Unlike pyrite it doesn't seem to vary much between sites or occurrences.
Famously it was combined with zincite to build bi-crystal "Perikon" detectors, invented in 1908 by Greenleaf Whittier Pickard.