Chemically, limestone is largely composed of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate. Ordinarily it is in white shades but may be colored due to impurities like iron oxide making it brown, yellow or red and carbon part making it blue, black or grey. Generally, its texture varies from coarse to fine.
At present most of the limestone are similar in chemical and mineralogical composition, the intricate organic and chemical part of carbonate sediments lead to a wide range of textures and fabrics in the resulting lime stones. It is commercially used in building materials and as a source for industrial and agricultural lime.
Some of the limestone is composed from skeletal fragments of marine organisms such as coral or foraminifera. In industries it is used as flux in extraction of iron and as an ingredient in Portland cement. It is also used in as aggregate for the base of roads, as white pigment or filler in products like toothpaste or paints and as chemical feedstock. Its various varieties are present in market like marl, chalk, dolomite travertine, and marble. In addition limestones and dolomites are important reservoirs for oil and gas.