Elementary carbon the first serious attempts at producing synthetic diamonds were made at the end of the nineteenth century by Hannay in Britain and Moissan in France, with uncertain, but probably negative, results. The first sure successes were achieved in 1953 in Sweden, 1955 M the United States, and probably about the same time in the Soviet Union. Production is now estimated to exceed 100 million carats a year, equal to about two-thirds of the industrial diamonds used.
Always in minute, polyhedral crystals, with well developed octahedral, cubic or even rhombic dodecahedral faces, from a few hundredths of a millimeter to about a millimeter in size, this being predetermined as far as possible by adjusting the environment and period of growth. Around 1970, stones weighing about one carat each uncut were also produced experimentally in the United States, using other, smaller diamonds as a raw material. Colored specimens in blue, yellow, and gray were also obtained. These diamonds, with clearly defined, cubic or octahedral faces, were of a suitable size and quality for use as gems.
Identical to those of natural diamonds: hardness 10; density 3.52 g/cm3; refractive index, about n 2.42; perfect octahedral cleavage.
Synthetic diamonds (for industrial uses) are now manufactured by many companies worldwide: in the United States, the Soviet Union, Japan, China, India, Holland, Finland, South Africa, Sweden, and Ireland (the industries in the last three countries mentioned are related to the De Beers group).
Very few gem quality synthetic diamonds have been produced. Their cost being extremely high some of them are housed at the Smithsonian Institution in Washington. Unless one is involved in their production, the chances of coming across a specimen are slim.
A few of these diamonds have been cut into ovals or brilliants, weighing 0.25-0.40 carats. With others, the spontaneous facets have merely been polished to make them perfectly transparent, maintaining their slightly flattened cubic shape, with small, octahedral faces. Some are colorless or almost so; others, yellow, light blue, or grayish.
One cannot generalize from so few examples, but the inclusions are apparently different from those of natural diamonds.
They are not found on the market, having been produced solely for research purposes. But they apparently cost much more than good quality natural diamonds of similar characteristics.