Ancient civilization were fascinated by the exceptional hardness of diamond, although colored gems were regarded as more aesthetically pleasing. Diamond was extremely rare up to the eighteenth century and was only fully appreciated after the modern type of brilliant cut, which shows it in all it glory, was developed at the beginning of the twentieth century. It is the most important gemstone today. Statistics a few years ago showed that diamonds accounted for 80% of the movement of money generated by gemstones. About 2 million carat of cut diamonds are issued on the market each year (it is the only gemstone for which reliable statistics are available), equal to a volume of little more than 110 liters.



Distinctive features:
Hardness can be an important facture in distinguishing diamond from other stones. It is infact the only gemstone capable of scratching corundum. The best modern imitation, cubic zirconia’s is less hard than corundum, so the two can easily be distinguished by comparing them with corundum, although the results of the tests must be observed under a binocular microscope or atleast a lens. Diamond’s exceptional hardness is also displayed by the facet edges, which are sharper than in imitations. This is best appreciated in relation to zircon, which has brittle, easily damage edges, and the less hard imitations such as synthetic rutile and strontium titanate. If the stones are turned between the thumb and forefinger, the two softer substitutes feel more slippery, almost oily, compared with diamond, because of this difference in edges. Another characteristic can be seen in the girdle, but only when it is not faceted. Due to the procedure used in turning brilliant cuts, the girdle of a diamond will have a satiny finish, similar to that of finely ground glass (in recent years, a similar effect has been achieved with cubic zirconia, but no other imitation display this). Also, when there are numerous flaws like minute cracks standing from either side of the girdle (these are known as “bearding” and are due to inexpert turning of the rough stone), it is bound to be diamond. A brilliant cut can display smart facets on the girdle to extending from the girdle toward the pavilion (or more rarely, toward the crown), these are the remains of the outer surface of the uncut octahedron (nearly always with minute, crystallographically oriented shallow triangular cavities), or of the faces of octahedral cleavage. In the later case, small steps can be observed between contiguous, secular’s plane surfaces. However, these details are only readily visible if magnified atleast 10/20 times. Sometimes small triangular facets alone are seen extending from the girdle. Called extra facets or supplementary facets, these are produced by polishing of the facets just described or by the elimination of some small, almost superficial flaw. Although very similar to the foregoing and not usually found on imitations, these facets are less distinctive in that they could be produced on any other stone.



Occurrence:
Gem quality diamonds are found in about twenty different countries, a dozen of which are in Africa, three in Asia, one in Occeania, and three in South Africa. By far the largest producer in South Afrca, including the neighbouring Lesotho, Botswana, and Naimibia. Next come the Soviet Union, Angola, Zaire, and Sierra Leone. Other important areas are the central African republic, Tanzania, Ghana, and Venezuela, with Australia and Brazil further behind, and India now one of the last.



Value:
Diamond is one of the most valuable stones, together with ruby and emerald. The market value of diamonds is determined by complex grading systems that divide them into a wide range of different categories. The basic characteristics considered are weight, color, and purity. Less crucial factors are the proposition of the cut and the surface finish.



Simulants and Synthetics:
Diamond has been imitated by glass and special glass with a mirror backing to increase reflection called “strass.” It has been imitated by the colorless, synthetic spinels and corundum ever since these began to be produced. Over the last few decades, moreover, it has been imitated by a whole range of synthetic and artificial products:
1.Strontium titanate or fabulite, which has much higher dispersion than diamond, with striking iridescence, low hardness, considerable brittleness and density.
2.Synthetic rutile or titania, which has very high dispersion with striking iridescence, marked birefringence, high density, and low hardness.
3.YAG (yttrium aluminum garnet), which has a slightly lower refractive index than diamond, a hardness of less than 9, and greater density.
4.GGG (gadolinium gallium garnet), which has a fairly low hardness and double the density of a diamond.
5.Cubic zirconia (cubic zirconium oxide), djevelite or phianite, the most recent and hardest to distinguish from diamond. Its density, however, is much greater, and its hardness is less than nine.
Many other artificial substances are similar to diamond, but are not used as imitations because there cost is generally much higher and their characteristic not better than those simulants already mentioned. Diamond has been and still is manufactured synthetically, in minute crystals, only suitable for industrial purposes. It has also been produced experimentally for use as a gemstone and a few gems of about 0.25/0.45 carats have been cut. But it is so hard to make the crystals grow that the cost would be much higher than that of natural diamonds obtained from known deposits.