Shane Elen

Spectral Reflectance and Fluorescence Characteristics of Natural-Color and Heat-Treated "Golden" South Sea Cultured Pearls

114 “GOLDEN” SOUTH SEA CULTURED PEARLS GEMS & GEMOLOGY SUMMER 2001 first marketed in 1993 with full disclosure that they were treated (Vock, 1997). Details of the proprietary process are not known, but it has been reported that the treatment, which is believed to be stable, is applied to undrilled cultured pearls and involves the use of heat without the application of dyes or bleaching (Vock, 1997). Inasmuch as the report did not exclude chemicals other than bleach, it is possible that chemicals also may be involved in the treatment. It is probable that other companies are treating “golden” pearls using a similar process. The challenge for the gem and jewelry industry is to separate natural-color cultured pearls, of any color, from treated ones (Sheung, 1998). Although, as noted above, drilled treated cultured pearls generally can be distinguished from natural-color cultured pearls by microscopy (Hargett, 1989), undrilled cultured pearls—especially in the absence of obvious visual features—are much By Shane Elen

Hydrothermal Synthetic Red Beryl from the Institute of Crystallography, Moscow

42 SYNTHETIC RED BERYL GEMS & GEMOLOGY SPRING 2001 both natural and synthetic, plus Ti, Co, and Ni in synthetic beryls; Sinkankas, 1981; Fritsch and Rossman, 1987). These elements substitute for Al. Alkali elements (Li, Na, K, Rb, Cs) can also occur in minor amounts by substituting for Be and Al (Sinkankas, 1981; Aurisicchio et al., 1988; Deer et al., 1997, pp. 378–386); however, these elements do not affect beryl coloration. The beryl crystal structure contains two different sites along “open” channels that can incorporate water molecules (Schaller et al., 1962; Wood and Nassau, 1968; Schmetzer, 1989; Deer et al., 1997). These variations in transition metal, alkali element, and water contents in beryls cause differences in physical properties (such as refractive index, specific gravity, and color), as well as in visible and infrared absorption spectra.

Synthetic Moissanite: A New Diamond Substitute

GEMS & GEMOLOGY Winter 1997 o the long list of diamond simulants currently available in the jewelry market, a new one has been added: synthetic moissanite. As typically happens with the introduction of a synthetic or simulant, there is considerable concern in the jewelry trade about this diamond imitation and its identification. One particular problem with synthetic moissanite is that its thermal properties are so close to those of diamond that it passes as “diamond” when tested with a thermal probe. This article reports on the examination of several samples of near-colorless synthetic moissanite (figure 1), both to characterize this material and to determine how it can be identified by standard gem-testing methods. The authors also evaluate a testing instrument developed by C3 Inc., which is intended to be used in conjunction with a thermal probe to distinguish this new simulant from diamond.

Identification of Yellow Cultured Pearls from The Black-Lipped Oyster Pinctada Margaritifera

66 NOTES AND NEW TECHNIQUES GEMS & GEMOLOGY SPRING 2002 colored strands marketed today may include a mix of cultured pearls from the P. maxima and P. margaritifera (Federman, 1998b) or consist only of cultured pearls that originate from the P. margaritifera. The latter may include several in the following yellow hue range: yellow, greenish yellow, brownish yellow, or grayish yellow. This makes some of them difficult to distinguish from similar-color cultured pearls from the P. maxima. Identification of the mollusk species in which a pearl was cultured is becoming an important issue in the industry. Until recently, it was relatively easy to identify freshwater, South Sea, “Tahitian,” or Akoya cultured pearls just by size, shape, and color. Today, however, there is considerable overlap in these once distinctive characteristics from one type of cultured pearl to another. Yet guidelines for quality grading cultured pearls often vary with the mollusk species. For example, the acceptable nacre thickness for the export of black cultured pearls from Tahiti is 0.6 mm (scheduled to change to 0.8 mm on July 31, 2002; “Pearl thickness controls...”, 2001). This would be exceptional for an Akoya cultured pearl (grown in the Pinctada fucata martensii), as it would require a culturing period of about By Shane Elen

Update on the Identification of Treated "Golden" South Sea Cultured Pearls

BACKGROUND Recently, UV-Vis reflectance spectroscopy was used to help distinguish natural-color “golden” cultured pearls from those reportedly treated using heat (Elen, 2001). The application of this “heat” treatment method to undrilled pearls was unlike the more common dyeing method encountered by gemologists, which typically is applied after drilling, often resulting in a characteristic concentration of color in the drill hole. Evidence of the “heat” treatment method in undrilled pearls occasionally could be detected by observing an unusual color concentration in surface defects, or was indicated by the atypical fluorescence. However, testing of known natural-color samples has revealed that both yellow shell nacre and natural-color “golden” cultured pearls from the Pinctada maxima mollusk exhibit broad absorption from 330 to 460 nm (Elen, 2001). This absorption was found to consist of two features, one in the UV region from 330 to 385 nm and a weaker one in the blue region of the visible spectrum from 385 to 460 nm. Closer examination of these features showed absorption maxima between 350 and 365 nm and from 420 to 435 nm. The strength of both these absorption features increased with increasing saturation of the yelBy Shane Elen

Russian Synthetic Ametrine

Gem-quality synthetic ametrine has been produced commercially in Russia since 1994, by hydrothermal growth from alkaline solutions. Faceted synthetic ametrine has many similarities to its natural counterpart from Bolivia. For the most part, however, the synthetic ametrine obtained for this study could be identified by a combination of characteristics, including growth features such as twinning and color zoning. EDXRF chemical analyses revealed higher concentrations of K, Mn, Fe, and Zn than in natural ametrine. IR spectra of the synthetic citrine portions showed more intense absorption in the 3700-2500 cm^(-1) range compared to natural ametrine; the synthetic amethyst zones showed a weak diagnostic peak at 3543 cm^(-1).

MULTICOLORED BISMUTH-BEARING TOURMALINE FROM LUNDAZI, ZAMBIA

LOCATION AND ACCESS The multicolored tourmalines described in this report were found in a field in the Kalungabeba area of the Lundazi district (figure 2), about 16 km (10 miles) southwest of Lundazi itself, according to Mr. Sarosi, who visited the site in early 1997. The stones were originally discovered by a person who was digging a hole for an outhouse. A rough dirt road leads to this site from Lundazi; it is best traveled by four-wheel-drive vehicle. During the rainy season, from about late December until March, the area is often inaccessible.