basic copper carbonate

Copper(II) carbonate (often called copper carbonate or cupric carbonate) is a blue-green compound (chemical formula CuCO3) forming most of the patina one sees on weathered brass, bronze, and copper. The colour 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. It was formerly much used as a pigment, and is still in use for artist's colours. It has also been used in some types of make-up, like lipstick, although it can also be poisonous to humans. It also has been used for many years as an effective algaecide in farm ponds and in aquaculture operations.
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