Marble

"A metamorphic crystalline rock composed predominantly of crystalline grains of calcite, dolomite, or serpentine, and capable of taking a polish"

Marble is generally formed from limestone undergoing metamorphism. When exposed to extremes of pressure or heat limestone turns into calcite or dolomite crystals. Marble has been used in architecture and sculpture from as far back as the Ancient Greeks, and is still used heavily today in many construction projects.