Marble...

  Marble is a metamorphic rock resulting from the physical and chemical changes of limestone composed mostly of calcite ( calcite is a crystalline form of calcium carbonate). Marble is extensively used for sculpture, building materials, countertops and many other applications.

  The characteristic swirls and veins of many colored marble varieties are usually due to various mineral impurities such as clay, silt, sand, iron oxides, or chert which were originally present as grains or layers in the limestone. Pure white marble is the result of metamorphism of very pure limestones. Colorless or light-colored marbles are a very pure source of calcium carbonate, which is used in a wide variety of industries. Finely ground marble or calcium carbonate powder is a component in paper, and in consumer products such as toothpaste, plastics, and paints .