Gem-quality synthetic diamond crystals weighing up to 11 ct have been grown in limited numbers at the De Beers Diamond Research Laboratory since the 1970s. These crystals have been produced strictly on an experimental basis and are not commercially available. Examination of a group of 14 brown1s17 yellow, yellow, and greenish yellow synthetic diamonds reveals distinctive gemological properties: uneven color distribution, geometric graining patterns, metallic inclusions, and, i n most cases, fluorescence t o shortwave but not to long-wave U.V radiation.

The distinctive gemological properties of the gem-quality synthetic yellow diamonds grown by Sumitomo Electric Industries are described. These synthetic diamonds, produced on a commercial basis, are grown as deep yellow single crystals i n sizes up to 2 ct. The material i s currently marketed for industrial applications only, in pieces up to about 0.40 ct. The synthetic diamonds can be distinguished by their ultraviolet fluorescence (inert to long-wave; greenish yellow or yellow to shortwave); their unusual graining, veining, and color zonation under magnification; and the absence of distinct absorption bands in their spectra.

The existence of gem-quality synthetic diamonds and their potential impact on the marketplace has long been a source of concern to gemologists and gem dealers the world over. While w e do not know whether cuttablegem-quality diamonds have been synthesized in other nations, we do know that the General Electric Company has successfully synthesized cuttable gemquality diamonds i n the United States. Eight of these diamonds were studied i n an attempt to determine means of identifying them using standard gemological tests. Sophisticated chemical and X-ray diffraction analyses and spectrophotometric and ferromagnetic studies were also performed. Distinctive inclusions, absence of strain in polarized light, electrical conductivity, and absence of both an absorption spectrum and a reaction to long-wave ultraviolet radiation were found to be useful indicators. Magnetism was also found to be a positive basis for separation but is not practical for the jeweler/gemologist.

helped with the chemical analyses. The assistance of Eli Haas and Martin Rapaport was invaluable. Unless otherwise noted, all pholomicrographs are by John I. Koivula. This study was supported in part by the Dr. Byron C. Butler Fund for tnclusion Research.

Significan~ deposits of gem-quality peridot hove been found i n the People's Republic of China. This Chinese peridot has geologic origins and gemological properties almost identical to the peridot fo~lnd on the San Carlos