Limestone is the most commonly used agricultural liming material. Chemically it is calcium carbonate. It is a naturally occurring sedimentary rock.  Lime is prepared by crushing limestone to a fine powder. Good quality lime stone has 37–40 % Calcium.

The efficiency of liming materials is said in terms of neutralizing value. The neutralizing value of 100 per cent pure lime stone is 100.

The fineness of the liming material is important in determining how quickly it reacts with soil acidity. Liming materials of a smaller particle size reacts quickly. It will be exposed to more surface area for chemical reaction.

The fineness of liming material is measured based on sieve test. Liming materials passing through a 60 mesh sieve will give 100 per cent efficiency. And materials passing through sieve of 20 mesh size but not of 60 will give an efficiency of 60 per cent. Those above 8 mesh sieve but below 20 will have an efficiency rating of 20 per cent.