Photo of peacock ore

A - D

Chalcopyrite

Chalcopyrite is a mixture of copper, iron and sulphur. In this more copper-rich form, it should really be called bornite, but is probably better known as peacock ore. You can see why. The bright colours are down to a tarnish that forms fairly quickly on exposed surfaces. These are from Mapimi, in Durango, Mexico. 

3-4cm