Mineral Species: Chalcocite

Chemical Formula: Cu2S

Chemical Name: Copper Sulphide

Mineral Class: Sulphide

Mineral Notes: Chalcocite is an important copper ore. It is one of the most profitable copper ores because the copper content is very high and because of the ease at which copper can be separated from sulphur. The mineral is secondary, usually laid down by secondary enrichment of original copper deposits. It usually forms above the water table where primary ores are altered by oxygen. Consequently ore bodies will have a layer of Chalcocite which corresponds to the present or a past water table level and this layer is called a 'chalcocite blanket'. Because Chalcocite is a secondary mineral it often forms pseudomorphs after many earlier primary minerals.

Description: Dark grey crystals of Chalcocite embedded in matrix. They have a strong metallic luster and appearance, due to the high copper content. The red-brown matrix provides an aesthetic contrast for the mineral. The specimen is rare because of its location.

Location: Wheal Basset, Illogan, Cornwall, England.