A metamorphic, hard, dense, crystalline stone primarily composed of calcium carbonate; it is limestone or dolomite that has been metamorphosed with heat and pressure. Pure calcite marble is white, but impurities produce a wide variety of coloring and patterns. It is finely grained and polishes to a smooth, high gloss. It is used primarily for statuary and buildings. Marble has been quarried from sites around the world since at least the 7th century BCE. The term can also refer more broadly to any crystallized carbonate rock, including true marble and certain types of limestone, that will take a polish and can be used for architectural and ornamental purposes.

Source: AAT

http://vocab.getty.edu/page/aat/300011443