Calcite is a mineral that occurs in small amounts in most types of rocks and makes up the largest part of limestone and marble. Pure calcite is transparent or white, but a variety of impurities can give this mineral certain colors. Nickel impurities produce green calcite; manganese, pink calcite; and iron, brown calcite. Calcite in the form of limestone is the chief source of lime. Limestone also serves as a raw material in cement and mortar and as a building stone.