Marble is formed when limestone is heated and pressurized within the earth’s crust. It consists primarily of calcite and dolomite. Any impurities that are present in the limestone when it goes through its metamorphosis into marble affect the mineral composition, which ultimately gives marble its unique coloring, textures and veining. Green marble, for example, is loaded with serpentine, while red marble is the result of hematite getting into the mix. Yellow marble is full of limonite, and blue marble is diopside. The whiter the marble, the purer the limestone from which it has formed.