Cu2(OH)2CO3 4HCl==2CuCl2 3H2O CO2.

"Patina" is basic copper carbonate, which is malachite green in color, so it is also called malachite. It is a precious mineral gem. After the action of dilute hydrochloric acid, the patina gradually disappears and the solution turns green. Eventually carbon dioxide gas and copper chloride are produced.

Extended information

Basic copper carbonate is generally used in organic catalysts, pyrotechnics manufacturing and pigments. In agriculture, it acts as a preventive agent for plant smut, an insecticide and an antidote for phosphorus poisoning, and also acts as a fungicide for seeds; mixed with asphalt, it can prevent livestock and wild rats from chewing saplings.

Basic copper carbonate is stored in a cool, ventilated warehouse. Keep away from fire and heat sources; prevent direct sunlight; package sealed; should be stored separately from oxidants, acids, and food chemicals, and avoid mixed storage.

Reference: Baidu Encyclopedia-Basic Copper Carbonate