Copper is a reddish coloured metal which is malleable and ductile. It has excellent thermal and electrical conductivities and good corrosion resistance. It is found in sulphide ores and as carbonate, arsenide and chloride (abundance in the Earth's crust is 50 ppm). Extraction of the metal involves roasting the ore to produce the oxide, followed by reduction and purification by electrolysis. The element is inert to non-oxidising acids but reacts with oxidising agents. In air, it will weather to produce the characteristic green patina of the carbonate. Copper will combine with oxygen on heating to produce CuO at red heat, and Cu2O at elevated temperatures.