Marble

True marble was originally limestone that has been altered by heat and pressure over time. These materials originally deposited as unconsolidated sediments under water by chemical precipitation and by living organisms, have been buried, heated and subject to huge confining pressures over lengthy periods of time. Such processes of metamorphism have transformed the limestone to a denser, harder crystalline rock......Marble!
http://www.palladiostone.co.za/marble-slab-counter-tops/