<P> Diamonds prepared as gemstones are sold on diamond exchanges called bourses . There are 28 registered diamond bourses in the world . Bourses are the final tightly controlled step in the diamond supply chain; wholesalers and even retailers are able to buy relatively small lots of diamonds at the bourses, after which they are prepared for final sale to the consumer . Diamonds can be sold already set in jewelry, or sold unset ("loose"). According to the Rio Tinto Group, in 2002 the diamonds produced and released to the market were valued at US $9 billion as rough diamonds, US $14 billion after being cut and polished, US $28 billion in wholesale diamond jewelry, and US $57 billion in retail sales . </P> <P> Mined rough diamonds are converted into gems through a multi-step process called "cutting". Diamonds are extremely hard, but also brittle and can be split up by a single blow . Therefore, diamond cutting is traditionally considered as a delicate procedure requiring skills, scientific knowledge, tools and experience . Its final goal is to produce a faceted jewel where the specific angles between the facets would optimize the diamond luster, that is dispersion of white light, whereas the number and area of facets would determine the weight of the final product . The weight reduction upon cutting is significant and can be of the order of 50% . Several possible shapes are considered, but the final decision is often determined not only by scientific, but also practical considerations . For example, the diamond might be intended for display or for wear, in a ring or a necklace, singled or surrounded by other gems of certain color and shape . Some of them may be considered as classical, such as round, pear, marquise, oval, hearts and arrows diamonds, etc . Some of them are special, produced by certain companies, for example, Phoenix, Cushion, Sole Mio diamonds, etc . </P> <P> The most time - consuming part of the cutting is the preliminary analysis of the rough stone . It needs to address a large number of issues, bears much responsibility, and therefore can last years in case of unique diamonds . The following issues are considered: </P> <Ul> <Li> The hardness of diamond and its ability to cleave strongly depend on the crystal orientation . Therefore, the crystallographic structure of the diamond to be cut is analyzed using X-ray diffraction to choose the optimal cutting directions . </Li> <Li> Most diamonds contain visible non-diamond inclusions and crystal flaws . The cutter has to decide which flaws are to be removed by the cutting and which could be kept . </Li> <Li> The diamond can be split by a single, well calculated blow of a hammer to a pointed tool, which is quick, but risky . Alternatively, it can be cut with a diamond saw, which is a more reliable but tedious procedure . </Li> </Ul>

How long does it take carbon to turn into a diamond