Marble is metamorphosed (1) limestone (2) composed of very pure calcium carbonate, CaCO3. The softness of marble and its relative isotropy and homogeneity make marble very desirable for sculpture and building stone. Although marble comes from limestone, the temperatures and pressures necessary to form marble usually destroy any fossils that may have been present in the limestone.

Notes:
1- Metamorphism can be defined as the mineralogical, chemical and crystallographic changes in a solid-state rock, i.e. without melting, in response to new conditions of pressure and/or temperature, and/or introduction of fluids.

2- Limestone is a sedimentary rock, mainly composed of mineral calcite. The primary source of the calcite is usually marine organisms, which settle out of the water column and are deposited on the ocean floors as pelagic ooze (but see lysocline for information on calcite dissolution). Secondary calcite may also be deposited in super-saturated meteoric waters (ground water that reaches earth's surface as precipitation), as is evidenced by the creation of stalagmites and stalactites. Limestone makes up approximately 10 percent of the total volume of all sedimentary rocks.