Colored diamonds are caused by impurities such as nitrogen (yellow), boron (blue). With red diamonds being due to deformities in the structure of the stone, and green ones being the result of irradiation.
Diamond is the hardest naturally occurring substance, and is also one of the most valuable natural substances. Diamonds are crystals formed almost entirely of carbon. Because of its hardness, the diamond is the most enduring of all gemstones. They are among the most costly jewels in the world, partly because they are rare, Only four important diamond fields have been found - in Africa, South America, India, and the Soviet Union.