Diamonds are thought to have been first recognized and mined in India, where significant alluvial deposits of the stone could be found many centuries ago along the rivers Penner, Krishna and Godavari.
Diamonds have been known in India for at least 3,000 years but most likely 6,000 years.
Later in 1797, Smithson Tennant repeated and expanded that experiment.
Those properties determine the major industrial application of diamond in cutting and polishing tools. Because of its extremely rigid lattice, it can be contaminated by very few types of impurities, such as boron and nitrogen.
Combined with wide transparency, this results in the clear, colorless appearance of most natural diamonds.
In particular, nanocrystalline diamond aggregates were measured to be harder than any large single crystal diamond.
Those aggregates are produced by high-pressure high-temperature treatment of graphite or fullerite (C The hardness of diamond contributes to its suitability as a gemstone.
In the 20th century, experts in gemology have developed methods of grading diamonds and other gemstones based on the characteristics most important to their value as a gem.