Diamond.

The mineral diamond is a crystalline form of carbon. Diamonds are renowned for their superlative physical qualities, especially their hardness and their dispersion of white light into a rainbow of colors, known in the trade as fire, for which they have been highly prized throughout history. Industrially, diamonds are ideal material for cutting and grinding tools — common applications include the cutting surfaces of saw blades and drill bits. The De Beers Group has been the largest player in the diamond industry for over one hundred years. The company owns mines that produce some 40 percent of annual world diamond production, and controls distribution channels handling nearly two thirds of all gem diamonds. Some controversy over diamonds has been generated because of the monopolistic practices historically employed by De Beers including strict control of supply and alleged price manipulation, as well as the practice by some African revolutionary groups of selling conflict diamonds in order to fund their often violent activities.