Order online limestone and get it delivered. Calcium carbonate (CaCO 3) is the primary component of limestone, which is a SEDIMENTARY ROCK. As building stones and aggregate, and as the main component of Portland CEMENT and lime, carbonate rocks - and even marble, the metamorphosed near-equivalent of limestone - play a vital role in the CONSTRUCTION INDUSTRY. Additionally, limestone is utilised in glass manufacturing, as fillers, abrasives, soil conditioners and in the manufacture of a variety of chemicals.