Marbles are formed from limestone or dolomite that has undergone enough heat and pressure to get metamorphosized into a crystalline structure. This metamorphosis takes place when the weight of overlying material, pressure from crystal collisions and heat from the earth's core generate temperatures in excess of 1800ºF.
It has an interlocking or mosaic texture composed of crystalline grain of calcite, dolomite or both. Texture of marble depends on the form, size and uniformity of grains. The chemical constituents of marble determine the color of the marble. Generally calcite and dolomite marbles are of pure white color. Variations of whiteness of pure marbles are due to the mixture of foreign substances. Such impurities form bands, streaks and clouds. Black and grayish shades are due to graphite; pinks, reds are mainly due to the presence of manganese oxides or hematite.