Spring 2006 Gems & Gemology Lab Notes

EDITORS Thomas M. Moses and Shane F. McClure GIA Laboratory CONTRIBUTING EDITORS G. Robert Crowningshield GIA Laboratory, East Coast Cheryl Y. Wentzell GIA Laboratory, West Coast ored square tablet in figure 1. This Unusual Multicolored specimen was composed of six thin ASSEMBLED STONE sections, each of a different color—red, Although in some cases (such as orange, yellow, green, light blue, and backed opal) an assembled stone is cre- light purple—joined with colorless ated to increase the durability of a gem cement. The client told us that he had material, the more common purpose purchased this “rainbow stone” with of manufacturing assembled stones is the intent to market it for use in com- to deceive. Green synthetic spinel and mitment ceremonies for members of synthetic quartz triplets have long imi- the Rainbow Coalition, a prominent tated emeralds. Likewise, doublets civil rights organization. consisting of natural green sapphire The client wanted to verify the crowns and synthetic sapphire or syn- identification of each of the six sec- Figure 1. This unusual specimen thetic ruby pavilions have fooled many tions. Due to the nature of the assem- was assembled from slices of buyers, as the natural inclusions in the blage, the individual refractive indices synthetic ruby, synthetic quartz, crown mask the synthetic inclusions were easy to obtain. The light purple, and synthetic spinel. in the pavilion. green, yellow, and orange sections had Rarely, however, do we see assem- R.I.’s of 1.54. The red section had an bled stones created for other, more R.I. of 1.76, and the light blue section synthetic ruby, the light blue section artistic purposes. It was therefore very had an R.I. of 1.72. A combination of as synthetic spinel, and the remaining surprising to receive for identification standard and advanced gemological four sections as synthetic quartz. the nearly 6 mm transparent multicol- testing identified the red section as Wendi M. Mayerson Figure 2. Fingerprint-like inclusions such as these have been reported in several colorless to near-colorless diamonds known to have been HPHT treated (from figure 10 in T. M. Moses et al., Fall 1999 Gems & Gemology, pp. 14–22). From left to right, magnified 32×, 18×, and 13×. 54 LAB NOTES GEMS & GEMOLOGY SPRING 2006 DIAMOND With “Fingerprint” Inclusions Fingerprint-like inclusions are common features in many colored stones, such as ruby and sapphire, but they are extremely rare in diamonds. In corun- dum, these “fingerprint” patterns are formed by fluid-assisted partial healing of pre-existing fractures. However, in the case of diamond, much higher pressures and temperatures are neces- Figure 3. This fingerprint-like Figure 4. A fingerprint-like inclu- sary to promote partial healing of frac- inclusion extends from a graphi- sion seen recently in this 0.64 ct tures and, at these conditions, fluids tized crystal in a colorless dia- natural-color Light blue diamond are usually not present. A few mond that was recently proved actually consists of groups of instances of fingerprint-like patterns to have been HPHT treated. many tiny crystals. Magnified 45×. produced by groups of tiny inclusions Magnified 45×. in natural-color blue and colorless diamonds have been reported, but the healed fractures in natural, untreated interconnected channel-like structure sisting of several groups of tiny crys- diamonds. that is common to sapphire “finger- tals, very similar to those described in The geologic environment in which prints” was not observed in these the 1968 and 1993 Lab Notes refer- these two diamonds may have been stones (see Lab Notes: Spring 1968, pp. enced above, was observed in a Light heated to the temperatures necessary 278–279; Spring 1993, pp. 47–48). blue, 0.64 ct, type IIb marquise bril- to cause partial healing of fractures In recent years, fingerprint-like liant (figure 4). However, the most remains a mystery. The heating must inclusions seen in colorless to near- intriguing discoveries were two color- have occurred very deep in the earth colorless diamonds are most often less type IIa diamonds (a 2.28 ct D- (i.e., at high pressures), in that the clar- associated with high pressure, high color round brilliant and a 1.00 ct F- ity of these relatively large gem-quality temperature (HPHT) treatment (figure color pear shape) that contained inclu- diamonds did not show any evidence of 2; see also T. M. Moses et al., “Obser- sions with an appearance remarkably the intense graphitization that occurs vations on GE-processed diamonds: A similar to the “fingerprints” seen in in diamonds heated at lower pressures. photographic record,” Fall 1999 Gems rubies and sapphires (figure 5). The These samples also serve as a caution & Gemology, pp. 14–22). Similar to diamonds were tested very carefully to gemologists that fingerprint-like fea- the HPHT-treated stones described in and determined to be of natural color. tures in colorless or near-colorless dia- Moses et al., a small “fingerprint” The channel-like patterns (not com- monds do not always mean the stones extending from a graphitized inclu- posed of tiny crystals) very strongly have been HPHT treated. sion was recently seen in an F-color, suggested that these were partially Christopher M. Breeding 4.79 ct, type IIa heart-shaped brilliant that was found to have been HPHT treated (figure 3). Figure 5. These fingerprint-like inclusions seen in two natural-color type Over the past few months, the IIa colorless diamonds show a channel structure that is remarkably simi- West Coast laboratory has had the lar to the “fingerprints” commonly found in ruby and sapphire. Magnified opportunity to examine three natural- 45× (left), 30× (right). color diamonds with a range of fingerprint-like inclusions. A pattern con- Editor’s note: The initials at the end of each item identify the editor(s) or contributing editor(s) who provided that item. Full names are given for other GIA Laboratory contributors. GEMS & GEMOLOGY, Vol. 42, No. 1, pp. 54–61 © 2006 Gemological Institute of America LAB NOTES GEMS & GEMOLOGY SPRING 2006 55 ilar pink glide planes, it contained a mation of the diamond lattice (see, Pink Diamond with Etch high concentration of nitrogen, most- e.g., A. T. Collins, “The colour of dia- Channels at the Intersections of ly in the A-form aggregation, and a rel- mond and how it may be changed,” Glide Planes atively weak platelet peak around Journal of Gemmology, Vol. 27, 2000, Pink graining and pink glide planes are 1365 cm−1 in the infrared absorption pp. 341–359). A glide plane is a distor- the main causes of a pink-to-red body- spectrum. As expected, the UV-visible tion of the crystal lattice, with the car- color in natural diamond. In contrast to absorption spectrum displayed moder- bon atoms shifted away from their pink graining, which is usually rather ately strong and sharp absorptions at normal, stable positions. This distor- irregular in morphology, the glide 316, 330, and 415 nm (N3), and a broad tion would be significantly intensified planes typically occur as a set of well- band centered at ~550 nm. where the two sets of glide planes defined, parallel, and highly color-con- The distance between individual intersect, since it is occurring in two centrated planes that extend through planes varied from about 0.2 to 1.0 separate directions. The carbon atoms the entire stone or a large part of it. In mm. The two sets of planes were near- in these strongly distorted regions our experience, only a few percent of ly perpendicular to each other (again, would not have a normal diamond pink diamonds are colored by glide see figure 6), and etch channels were structure, and thus they would not be planes, and pink stones of this type observed where the two sets intersect- chemically as stable. As a result, dis- usually have only one set. However, ed. All the channels were likewise solution or etching could selectively the East Coast laboratory recently straight and parallel. Depending on occur in these regions. examined a pink diamond that had two the development of the glide planes, Etch channels are a common sets of glide planes (figure 6), as well as the dissolution channels varied from sight in natural diamonds, though etch channels that occurred at the less than 1 mm to over 2 mm deep. their formation mechanisms are not intersections of the planes. This feature The shape and diameter of the chan- fully understood (see, e.g., T. Lu et al., is not only rare among pink diamonds, nels were too small to be determined “Observation of etch channels in sev- but it also supplied an opportunity to with a regular gemological micro- eral natural diamonds,” Diamond examine the mechanism by which scope, but the diameter appeared to be and Related Materials, Vol. 10, 2001, etch channels form in diamond. less than 50 µm. Nevertheless, the pp. 68–75). This unusual pink stone The 0.77 ct round brilliant cut channels were readily seen with prop- revealed that intersections of plastic (5.87 × 5.76 × 3.61 mm) was color grad- er lighting (figure 7). deformation planes are chemically ed Light pink. Two large fractures The physics of the crystalline less stable, so they are one of the local- were present at the girdle. The dia- defect that generates the ~550 nm ities where etching can selectively mond displayed a weak blue fluores- broad absorption band is not well occur. cence to long-wave ultraviolet (UV) understood. However, it is widely Wuyi Wang, Vinny Cracco, radiation and was inert to short-wave believed to be related to plastic defor- and TMM UV, with no phosphorescence.

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