Copper ( II ) carbonate is a blue-green solid . Copper ( II ) carbonate ( often called copper carbonate or cupric carbonate ) is a blue-green compound ( chemical formula CuCO3 ) forming part of the verdigris patina that is found on weathered brass , bronze , and copper . The color can vary from bright blue to green , because there may be a mixture of both copper carbonate and basic copper carbonate in various stages of hydration .