Note:  Do not rely on this information. It is very old.

Copper Pyrites

Copper Pyrites, or Chalcopyrite (Cu2SFe2S3), though not containing more than 35 per cent. of copper, is, on account of its abundance, the chief commercial source of copper. It is generally massive or in minute crystals which are commonly tetrahedra of the Pyramidal system and are often twinned. It is metallic and brass-yellow, often with an iridescent or "peacock" tarnish. Its hardness is 3.5 to 4, which distinguishes it from iron-pyrites and makes it incapable of giving a spark with steel, whilst its brittleness distinguishes it from gold, as also does its comparative lightness. Its gravity is a little over 4. The darker its colour, the richer is the ore in metallic copper. When heated it decrepitates and gives fumes and sublimate of sulphur and a magnetic globule. It abounds in the Cornish mines and in most other copper-yielding regions.