Quicklime

Quicklime, also known as burnt lime, is mainly composed of calcium oxide. The usual method of making it is to calcine natural rocks whose main component is calcium carbonate at high temperature, which can decompose into carbon dioxide and calcium oxide.
Any natural rock with calcium carbonate as the main component, such as limestone, chalk, dolomite limestone, etc., can be used to produce lime. In coastal areas, shells are used as raw materials, which are burned into shell ash for use as quicklime.