Marble is a metamorphic rock, formed by the alteration of limestone under high temperature and/or high pressure. Marbles formed from pure calcite limestones are white, with a sugary texture, and they effervesce when tested with dilute (~10%) hydrochloric acid. Impurities in the limestone may lead to the formation of new minerals, giving the marble a variety of colours. Stonemasons often give the name marble to any rock that takes a good polish, but this is incorrect in geological terminology.

A famous white marble comes from Carrara in the Italian Appenines where it has been quarried for two thousand years. It is probably the finest in the world for sculpture, and has been used by famous sculptors such as Donatello, Michelangelo and Canova for their masterpieces. The Taj Mahal in India is built of white marble from Makrana.

Colour: may be uniformly white and glistening, light brown or grey; also variegated with green, red or black.
Mineralogy: 95% calcite (CaCO3) or dolomite Ca,Mg(CO3)2. Impurities may give rise to new minerals such as olivine.
Composition: calcareous.
Texture: medium to coarse grained, often showing a sugary texture.