Limestone is one of the most important of all the sedimentary rocks. Limestone is composed largely of calcium carbonate (CaCO3) in the mineral form calcite, but there are several other important carbonate minerals with which limestone is associated. Limestone is usually gray, but it may also be white, yellow or brown. It is a soft rock and is easily scratched. It will effervesce readily in any common acid. There are many different types of limestone formed through a variety of processes. Limestone can be precipitated from water (non-clastic, chemical or inorganic limestone), secreted by marine organisms such as algae and coral (biochemical limestone), or can form from the shells of dead sea creatures (bioclastic limestone). Some limestones form from the cementation of sand and / or mud by calcite (clastic limestone), and these often have the appearance of sandstone or mudstone. There are many products that are made of limestone: breakfast cereal, paint, calcium supplement pills, a marble tabletop, antacid tablets, high-quality paper, white roofing granules, and Portland cement. It can be used as a building material. Certain types of limestone are suitable for direct use as building stone. It is used in the production of cement by heating powdered limestone with clay. It is a major ingredient in toothpaste. It acts as a filler and white pigment.
It can be used as a food additive to provide calcium ions for strong teeth and bones.
Calcium carbonate the content of limestone rocks used as filler in manufacture of white paper. It increase the brightness of paper. Very high-grade limestone deposits with a calcium carbonate content over 95% used as fillers in manufactured goods such as, plastics, cleansers and carpets. Limestone deposits with a calcium carbonate content around 90% can be quarried to be used by the farming sector. By crushing the limestone, various grades can be produced. These products are marketed as ‘agricultural lime’.