Identifying Copper Minerals

Flame Test. An oxidized compound of copper when introduced into the flame gives it a vivid green flame color due to the copper oxide volatilized. When the mineral is moistened with hydrochloric acid and then heated, the flame color is an intense blue. If the mineral is a sulfide, it must be roasted in the oxidizing flam before moistening with hydrochloric acid and then heated, the flame color is an intense blue. If the mineral is a sulfide, it must be roasted in the oxidizing flame before moistening with hydrochloric acid.

Blue Solution with Ammonium Hydroxide. If an acid solution containing copper is made alkaline with ammonium hydroxide, it will assume a deep blue color.

Reduction to Metal on Charcoal. When a small amount of a copper minerals is mixed with a flux (best equal parts of sodium carbonate and borax), placed on charcoal and heated intensely in the reducing flame, metallic globules of copper will be formed. They are difficulty fusible, bright when hot, but become coated with an oxide coating on cooling. The are malleable and show the characteristic copper color. Sulfides of copper must first be roasted in the oxidizing flame in order to remove the sulfur before mixing with the flux.