Diamond

Diamond is a mineral form of pure carbon whose atoms are arranged in a crystal structure called diamond cubic. It has the highest hardness and thermal conductivity of any natural material, which is why it is used in cutting and polishing tools as well as in jewelry, and it is colorless in its pure form. A small number of impurities or defects can tint a stone blue (boron), yellow (nitrogen), brown (defects) or green (radiation exposure). Most natural diamonds are between 1 billion and 3.5 billion years old and formed 150 to 250 kilometres down in the Earth's mantle, then were carried to the surface in volcanic eruptions and deposited in rocks known as kimberlites and lamproites. Graphite is the stable form of carbon at room temperature and pressure, and diamond converts to it only at a negligible rate. About 80 percent of mined diamonds are unsuitable as gemstones and are used industrially.