What is a marble in geology ?

Marble : definition

In petrography, a marble is a metamorphic rock resulting from the transformation of limestones or dolomites by general or contact metamorphism. This phenomenon is essentially reflected by recrystallization of the calcite. When the limestone is impure, this recrystallization causes the migration of impurities which concentrate and recrystallize in various minerals scattered in the rock : these are the mineral marbles, sometimes called cipolins (marble with diopside, chondrodite, phlogopite, grossular, vesuvianite, etc...).

A marble can thus alternate chemically very pure zones with calcite alone, purer than the original limestone, and zones where mineralogical impurities are concentrated, which it is sometimes possible to eliminate by an appropriate treatment.

In the ornamental rock industry, however, this definition has been extended to any limestone rock capable of taking a fine polish and of being used in ornamentation. This second acceptance has no petrographic meaning : the "marbles" are then not always metamorphic limestones.