Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Marble was formed from limestone that underwent metamorphosis from intense heat and pressures within the surface of earth. This altered its crystalline structure and introduced other mineral impurities such as clay, silt, sand, iron oxides, or chert which were originally present as grains or layers in the limestone. The characteristic swirls and veins of many colored marble varieties are usually due to this factor.
Marble comes in a wide variety of colors and with different veining and sizes.
Commercially, any stone that can undergo a polish (except granite) is termed marble. This includes travertine, onyx, serpentine and limestone. Serpentine gives a green colour to the marble.