The composition of calcite is CaCO3, and it is a type of carbonate mineral. It often contains magnesium, iron, manganese and zinc. It belongs to the trigonal crystal system, and the crystals are rhombohedral or scalenohedral. The combinate form has spiked or tooth shapes. The aggregates can be in crystalline clusters, granular, stalactitic, oolitic, dense lumps or travertine forms. It can be colourless or white but often is coloured due to impurities. Colourless calcite is called ‘ice island stone’ in Chinese. It has a vitreous to pearly lustre, a specific gravity of 2.71, a Mohs hardness of three and sub-conchoidal fractures. Calcite forms in many types of rocks but commonly in limestone and marble.