Burnt lime (Calcium oxide) is also known as quicklime. It is derived by heating limestone to expel carbon dioxide. It is more concentrated and caustic than agricultural lime.

Calcium oxide is usually made by the thermal decomposition of materials such as limestone, or seashells, which contain calcium carbonate in a lime kiln. This is accomplished by heating the material to above 825 degree C.

It has a higher neutralising value of 179. That means instead of using 179 gram of lime stone (Calcium carbonate) only 100 gram of burnt lime (Calcium oxide) is needed. Similarly, instead of using 179 gram Dolomite only 109 gram Calcium oxide is needed.