BLACK SAPPHIRE

Sapphire is usually blue, but some is so blue that it is classed as black. It is a variety of corundum (Al3O3) and derives it's colour from iron and titanium impurities. The titanium impurities which transform colourless corundum into black sapphire appear in the form of rutile (titanium oxide). Iron impurities are derived from hematite.

It is very hard (9 on the mohs scale) and has a very bright, diamond like sheen. It can be imitated by black glass or artificially coloured quartz (although these lack the sheen of the real thing).

BORNITE

It is a member of the sulphide group and is fairly soft (3 on the mohs scale). It is reddish brown when extracted but tarnishes when exposed to the atmosphere (then it's surface may be red, blue or purple).

It is named after Von Born, an Austrian mineralogist. It is also known as peacock ore due it's colourful appearance.

It is a secondary mineral and forms in association with chalcopyrite. It is an industrial source of copper and is mined extensively. Copper is used for wires and cables because is a good conductor of electricity and it can also be alloyed with zinc to form brass.

It may be found in igneous rocks in locations such as Tasmania (Australia), Cornwall (UK), Mexico, Peru and the Atacama desert (Chile).