Diamonds are chemically composed of elemental carbon and are the hardest known natural substances. Physically, industrial-grade diamonds are black in color, due to impurities, and gem diamonds come in a variety of colors, including colorless, red, yellow, orange, green, brown and blue. Diamonds have a high luster and high dispersion.
Industrial diamonds are used in grinding, cutting, polishing and drilling procedures. They are also frequently crushed to produce abrasive powders. Since demand for industrial diamonds exceeds the supply obtained from mining, synthetic diamonds are produced to meet the excess demand. Diamonds are the world's most popular gemstones. Of the $19 billion spent on gemstones in the United States in 2010, $18 billion was spent on diamonds, with less than one billion dollars being spent on colored stones.
The quality of a diamond gemstone is dependent on the four C's: color, cut, clarity and carat. The most highly valued diamonds are those that are completely colorless. Ideally, cut stones have faceted faces that are equal in size and identical in shape. The ideal clarity for a diamond is one which is free from internal flaws and inclusions, which are foreign material particles in the stone. Diamonds are sold by the carat, and small diamonds cost less per carat than their larger counterparts of equal quality.