India, cradle of precious stones, will remain with Borneo the only diamond producer in the world until the 18 th century. John proclaims that "the white throne of judgment last is cut in the diamond". The diamond is so precious that it is deified in the marvelous religious : for the Hindu Vedas "the diamond throne of Buddha is at the center of the World", while the Apocalypse of St. Diamonds colored in yellow, blue, green or red are the most popular and fetch sky-high prices. In jewelry, its price depends on its color, its brilliance, due to its high refractive index, and its fires, which reflect its strong dispersion of light. Diamond powder is used for polishing the diamonds themselves but also other gemstones. Indeed, diamond saws have a steel crown set with fragments of diamond crystals in order to cut glass, rocks and hard materials, it is again fragments of diamonds that allow drill bits to dig rocks, to achieve the wire drawing or truing of the grinding wheels. Only transparent and flawless diamonds, colorless or harmoniously colored in yellow, red, blue or orange are cut for jewelry : they remain in the minority compared to impure diamonds, dark in color, the "borts", in great demand in cutting industries, and partially produced by synthesis to compensate for the low level of mining production. Most frequently they are octahedra (up to 6 cm), sometimes dodecahedra, tetrahedra or cubes, with faces often striated and curved. Diamond is also found in detrital deposits deriving from the alteration of kimberlites ( conglomerates alluvium).
Diamond is a primary mineral brought up from the deep mantle by kimberlites, these ultrabasic volcanic rocks very rich in phlogopite and pyrope, which are put in place in the form of particular volcanic chimneys : "the pipes".
Combined with an exceptional refractive index at the origin of the luster ( adamantine) and its lights, they make diamond a legendary mineral, the most prized of precious stones. Its name comes from this hardness : from the Greek adamas (invincible). Diamond is the hardest of all known natural bodies (hardness of 10 on the Mohs scale).
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