What is Marble?
The word marble is from the Greek word that translates to “shining stone.” Natural marble comes from the metamorphism of carbonate, sedimentary rocks. Typically, these are dolomite or limestone. During the metamorphism, re-crystallization occurs in the carbonate mineral grains.
The rock that is produced through this process has interlocking carbonated crystals. The original sedimentary structures of the rock as it existed prior to this change are often destroyed or changed.
Why Colors Occur
The color of marble has much to do with impurities present when the metamorphism of the stone begins. Dolomite and limestone that contain very little silicate become the purer white marbles. All the swirls present in colored marbles are the result of the impurities in the rock layers. These mineral impurities that affect the marble’s color include sand, iron oxides, chert, clay, and silt.
A marble that results in a green color has high magnesium limestone content. It can also begin with dolomite containing impurities such as silica. When a rock goes through a metamorphism, it has high temperatures and intense pressures applied to it. This causes crystallization of the impurities, which makes them mobile and liquid. When the heated rocks cool down, the impurities are positioned in new areas of the stone and have different colors.
White marble was the choice of sculptors from ancient times. There are several reasons for this. First, the consistency of the material is more uniform so that it is less likely to shatter at weakened areas. White marble is a relatively soft stone, which allows for easier chiseling and shaping.
In construction, marble contains serpentine, calcite, or dolomite that can be polished. Any dimension stone for support of structures or as design features is given the designation of “marble” if it is composed of calcitic rock.
Modern marble installed in homes and businesses is sometimes an artificial product. This is called “cultured marble” which denotes it is manmade. It begins with marble dust that is combined with resins and cement to produce a dense product for counter tops and other surfaces.
The technical explanation of cultured marble is a cast polymer, which is a mixture of unsaturated polyester resin. This contains color pigments and inorganic particles. There are also cultured forms of granite, onyx, and other stones. Each is based on the materials that are added to the polymers. Engineered calcium carbonates are applied to yield cultured marble.
Cultured Marble Surfaces
A blend of polyester resin, fillers, pigments, and a catalyst produce cultured marble surfacing. These are combined and poured into a predesigned mold and allowed to set and harden.
Afterwards, a gel coat seals the product and gives it a smooth surface and shine. The gel coat is a very tough polymer, resistant to heat, stains, and scratches. It is also non-porous so bacteria and germs cannot penetrate the surface.
Manufacturers of cultured products have their own standards and formulas that yield a similar look from one product to another. Colors and design are maintained so that customers can choose a range, which varies slightly from one application to another. The catalyst causes a chemical reaction that produces the hardened polymer.
The cultured marble has to stay inside the mold for several hours to harden before it can be removed, trimmed, ground, and polished to design specifications. Upon inspection, the marble is ready for use on countertops and other surfaces.