Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It occurs in many colours, including clear, white, pink, blue, yellow, green, orange, and brown, though its purest form is colourless. The colours are often due to various impurities. Calcite forms in a variety of geological environments: it's found in sedimentary rocks, metamorphic rocks, and as a hydrothermal mineral. It's also common in cave formations like stalactites and stalagmites. Significant deposits are found in Mexico, the United States, Brazil, India, and China.