Calcite is one of the most abundant minerals on earth. Due to various impurities it occurs in a wide variety of different colours.
The shells of many sea organisms are formed from calcite which helps balance the amount of carbon dioxide (CO2) in the oceans. Organisms use calcium to create solid crystals of calcium carbonate which is the material their shells are made of. Without calcite many would not exist. CO2 is a colourless and odourless gas vital to life on Earth. Calcite is the most common form of calcium carbonate and the main constituent of limestone.