Basic copper carbonates
Copper in moist air slowly acquires a dull green coating because its top layer has oxidised with the air. Some architects use this material on rooftops for this interesting colour. The green material is a 1:1 mole mixture of Cu(OH)2 and CuCO3:
2 Cu (s) + H2O (g) + CO2 + O2 → Cu(OH)2 + CuCO3 (s)
Copper carbonate decomposes at 290 °C, giving off carbon dioxide and leaving copper(II) oxide:
CuCO3 (s) → CuO (s) + CO2 (g)
Basic copper(II) carbonate occurs naturally as malachite (Cu2(OH)2CO3) and azurite (Cu3(OH)2(CO3)2).