Lime is not usually available in nature in free state. It is chiefly prepared by burning limestone. Depending on the percentage of calcium carbonate (CaCO3) in limestone, lime is classified into A, B and C types, which are used for masonry work, mortar and plaster and white washing, respectively. The type C variety is also known as pure lime or fat lime. Class A variety is only available in slaked form, while class B and C are available in slaked as well as unslaked forms. Lime is also obtained by burning kankar, shells of sea animals and boulders of limestone from beds of old rivers.
The lime that is obtained from the calcination of pure limestone is known as quicklime. It mainly consists of oxides of calcium and it is not crystalline. It shows great affinity to moisture.