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 com- mon 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 heal- ing 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 dia- monds 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 finger- print-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. Con- sistent with other diamonds with sim- Figure 7. As can be seen here, etch channels developed at the Two Diamonds from the Figure 6. In this 0.77 ct Light intersections of the two sets of Same Octahedron pink diamond, the pink color is glide planes in the 0.77 ct Light Typically a diamond cutter will fashion clearly concentrated in two sets pink diamond. With reflected at least two stones from a single octa- of glide planes, which are nearly light, the planes appear as dis- hedral crystal; however, these stones perpendicular to each other. tinct lines on the polished faces. rarely remain together for long. One is × × Magnified 38 . Magnified 98 . commonly larger than the other, so the diamonds tend to get distributed in dif- ferent lots. Certain spectroscopic meth- ods can sometimes be used to detect similarities in once-contiguous stones, but natural zoning of impurities and lattice defects in colored diamond crys- tals often makes it difficult to match spectroscopic data from different parts of the crystal. Other techniques such as X-ray topography may have more potential (see I. Sunagawa et al., “Finge- rprinting of two diamonds cut from the same rough,” Winter 1998 Gems &
56 LAB NOTES GEMS & GEMOLOGY SPRING 2006 studying the formation and evolution of the fluids/melts that are essential for diamond formation in the upper man- tle. These inclusions usually occur in the fibrous coatings on some octahe- dral diamond crystals. Although such coated diamonds from the DRC/Zaire and Botswana have been described pre- viously (O. Navon et al., “Mantle- derived fluids in diamond micro-inclu- sions,” Nature, Vol. 335, 1988, pp. Figure 8. High-energy DiamondView UV fluorescence patterns from these 784–789), and we have recently report- two diamonds (left, 0.38 ct; right, 2.39 ct) are nearly perfect mirror images ed on a colorless diamond and a Fancy of each other, strongly suggesting that they were at one time part of the Dark brown-greenish yellow diamond same crystal. with carbonate micro-inclusions (Lab Notes: Winter 2004, pp. 325–326; Summer 2005, pp. 165–167), it is still Gemology, pp. 270–280; R. Diehl and stones (figure 8). Furthermore, the extremely rare to see a faceted gem dia- N. Herres, “X-ray fingerprinting rou- high-energy fluorescence pattern from mond with these inclusions through- tine for cut diamonds,” Spring 2004 the base of the smaller diamond was out the entire crystal. Gems & Gemology, pp. 40–57). almost a mirror image of that seen in The 1.58 ct translucent brown- The West Coast laboratory re- the larger, blocked stone. The correla- orange round brilliant in figure 9 was cently examined two partially pol- tion of their DiamondView images, submitted to the East Coast laborato- ished colored diamonds that appeared gemological observations, and spectro- ry for identification and origin-of-color to have been cut from the same piece scopic data indicates that these two determination. Upon examination, of rough. The stones had been sub- diamonds were indeed cut from the we saw fractures that appeared to have mitted at the same time, but for sepa- same octahedron. orange color concentrations. With the rate origin-of-color reports. One (0.38 Christopher M. Breeding microscope, we also observed exten- ct) consisted of the rough top of a sive surface graining (figure 10), as brownish yellow octahedron with well as micro-inclusions throughout only the cut base polished. The other the stone. was much larger (2.39 ct) and had Unusual Translucent Brown- Since this diamond was translucent, been blocked into a yellow cut-cor- Orange Diamond we used diffuse reflectance infrared nered rectangular modified brilliant. Micro-inclusions in diamond, such as spectroscopy to study the inclusions. As Unpolished surfaces on both dia- water and carbonates, are useful in seen in figure 11, absorption bands at monds showed abundant brown radi- ation stains. The diamonds exhibited similar strain patterns with cross- polarized light, and both showed Figure 9. This translucent 1.58 ct Figure 10. With reflected light × greenish yellow fluorescence to long- brown-orange diamond (7.20 (here, on the table facet), surface × and short-wave UV lamps. Infrared 7.09 4.76 mm) appears to owe graining was observed over most spectroscopy revealed that both its unusual hue to large amounts of the diamond in figure 9. × stones were type Ia with abundant of carbonate micro-inclusions. Magnified 40 . nitrogen impurities; the spectra were almost identical. These similarities suggested that at one time these two diamonds might have been part of the same crystal. In an effort to confirm this specula- tion, the diamonds were examined with a Diamond Trading Company (DTC) DiamondView, which uses a high-energy UV source to reveal differ- ences in the fluorescence of diamond growth zonations. Distinctive fluores- cence patterns were present in both
LAB NOTES GEMS & GEMOLOGY SPRING 2006 57 90, No. 2–3, 2005, pp. 428–440). These peaks are observed in natural diamonds and may also be attributed to artifacts from contamination within the frac- tures of this diamond, so their presence is probably unrelated to inclusions. Our examination of this unusual diamond allows us to infer some geo- logic conditions of its formation. The shift in the peak positions of quartz in the IR spectrum corresponds to a pressure of 1.5 GPa at room tempera- ture (see Schrauder and Navon, 1994). Extrapolating to a typical mantle tem- perature of 1,000°C would correspond to a pressure of 4.5 GPa, which falls within the diamond stability field. Therefore, the micro-inclusions in this diamond appear to have crystal- lized from fluids that were trapped during its growth in the upper mantle. As the mantle-derived fluids in the Figure 11. Diffuse reflectance IR absorption spectroscopy showed that diamond cooled during its travel to this diamond is type Ia with carbonate and water micro-inclusions. By the surface, they developed into a sec- subtracting the spectrum of a pure type Ia diamond, the absorption ondary-phase assemblage that formed bands of other micro-inclusions such as apatite and micas can be seen the micro-inclusions (i.e., water, car- in detail (inset). bonates, silicates, apatites, micas, and clays). This assemblage, with an
absence of molecular CO2, suggests 3420 and 1640 cm−1 suggested the pres- “Luminescence study of defects in that the diamond formed under con- ence of water molecules. A silicate synthetic as-grown and HPHT dia- ditions that were fluid-rich and gas- absorption band was also seen at 1065 monds compared to natural dia- poor. The inclusions correspond to cm−1. The two bands at 605 and 575 monds,” American Mineralogist, Vol. both carbonatitic fluids (carbonates) −1 cm are due to apatite (M. Schrauder and hydrous fluids (water, SiO2), and O. Navon, “Hydrous and carbon- which may coexist at upper-mantle atitic mantle fluids in fibrous dia- Figure 12. High-energy Diamond- temperatures and pressures. monds from Jwaneng, Botswana,” View fluorescence imaging shows Because this diamond was pol- Geochimica et Cosmochimica Acta, that the diamond in figure 9 grew ished, there was no obvious evi- Vol. 58, No. 2, 1994, pp. 761–771). The from a cube to an octahedron dence of its crystal habit. However, −1 bands at 812 and 785 cm are due to with multiple growth centers. when it was examined with the quartz. They are shifted from their nor- This was further confirmed by a DTC DiamondView, the fluorescence −1 mal positions at 798 and 779 cm as a distinctive cubic growth center image showed that the internal mor- result of the high internal pressure seen when the diamond was phology evolved from cube to octahe- within the micro-inclusions. The band viewed through the pavilion. dron with multiple growth centers at 840 cm−1 is characteristic of micas (figure 12). It also indicated that the and clay minerals. The bands for car- brown-orange color followed the 2- bonates (CO3 ) were also observed at growth zoning. This could be impor- 1430 and 876 cm−1; these are the main tant evidence that the color was carbonate band and the characteristic caused by micro-inclusions that were band for calcite, respectively (again, see captured by different growth zones Navon et al., 1988). rather than along the fractures as it The bands at 2965 and 2926 cm−1 initially appeared. Another Diamond- are caused by the CH2 group, the one at View image through the pavilion −1 2854 cm by the CH3 group, and the showed a distinctive cubic growth sharp peak at 3107 cm−1 is assigned to center, confirming that this diamond the C=CH2 group (J. Lindblom et al., grew from multiple growth centers.
58 LAB NOTES GEMS & GEMOLOGY SPRING 2006 Figure 14. The extent of the glue used to affix the emerald crystals in the matrix became very appar- ent when the specimen was exposed to long-wave UV radia- tion. Notice how visible the writ- ing in one of the crystals is.
The purpose of the examination was to make sure the emerald crystals were natural, as well as to document something very unusual that had been done to them. Spectroscopic testing and micro- scopic examination confirmed that the crystals were natural emeralds. Close observation of the specimen at the base of the crystals revealed an Figure 13. This emerald-in-matrix specimen was known to be assembled adhesive that had been mixed with prior to being submitted to the laboratory, but it proved to have another, crushed matrix to give it a more nat- very unusual, characteristic. ural appearance—a practice that is very common in the construction or reconstruction of mineral speci- mens. The glue was easily visible This brown-orange diamond is the when exposed to long-wave UV radi- first we have analyzed with this vari- Inscriptions Inside ation, as it fluoresced a strong blue ety of micro-inclusions. Advanced EMERALD Crystals (figure 14). spectroscopic testing not only con- Occasionally the laboratory receives This was not, however, the most firmed that its color was of natural mineral specimens for identification, interesting aspect of the specimen. The origin but also provided keys to its usually for the purpose of determining two largest crystals (26.75 × 25.50 × geologic formation. An orange hue is whether or not they are natural or 20.50 mm and 17.00 × 20.80 × 19.90 not common in naturally colored dia- have been assembled (see, e.g., Spring mm) had what appeared to be some monds; it is mainly due to the pres- 2003 Lab Notes, p. 42). The emerald- sort of internal inscription. With a ence of point and/or extended defects. in-matrix specimen shown in figure loupe, it could be seen that the writing This diamond demonstrated that 13 was submitted to the West Coast was in Arabic and was not on the sur- micro-inclusions may also contribute laboratory, but this time the owner face of the crystals. With the micro- to an orange coloration. knew in advance that it had been scope, the answer to this mystery Kyaw Soe Moe and Paul Johnson assembled from Colombian material. became clear. While out of the matrix,
LAB NOTES GEMS & GEMOLOGY SPRING 2006 59 47–48). This stone contained numer- ous oriented needles, which caused the star, so we concluded that the asterism was natural. What was unnatural, however, was the apparent color. When the bottom of the cabochon was viewed with magnification and a com- bination of overhead and darkfield lighting, a slightly uneven blue coating Figure 16. It appears that some was clearly visible. In fact, two small sort of material with Arabic writ- chips near the stone’s edge revealed ing was inserted into the holes colorless quartz underneath (figure 18). made in the two largest emerald Coating is one of the simplest crystals. Magnified 10×. ways to change a stone’s color and is frequently used on a variety of mate- rials, including diamond, beryl, topaz, cubic zirconia, and, of course, quartz. What made this particular ring inter- Color-Coated Star QUARTZ esting was that the color of the coat- Figure 15. This view through the Recently, the East Coast laboratory ing on the natural star quartz cabo- termination of one of the emer- received for identification a grayish chon created an extremely convincing ald crystals in figure 13 reveals blue oval cabochon displaying aster- imitation of a star sapphire. As noted that a hole had been drilled ism. The stone measured approxi- above, this is hardly a new material. down the center from the bottom mately 12.35 × 10.25 × 6.45 mm and GIA reported on a nearly identical without breaking the surface of was set in a white metal ring (figure stone—a star quartz with blue back- the termination. Magnified 10×. 17). Standard gemological testing ing added to imitate star sapphire—in revealed a spot refractive index of 1.54 the Summer 1938 G&G (p. 168), and a bull’s-eye optic figure, which which shows that no matter how identified the stone as quartz. many new treatments come on the the crystals apparently had been core The lab has reported on star quartz market, gemologists must still be on drilled from the bottom, with care many times over the years, discussing guard for simple ones such as this. being taken not to cut through the ter- the typical colors, cause of asterism, [Editor’s note: The Summer 1938 mination or any of the prism faces. and sources of the material (see, e.g., issue is available in PDF format on What appeared to be a rolled up piece of Lab Notes: Winter 1981, p. 230; Spring the Gems & Gemology website at paper or some other writing material 1985, pp. 45–46; Spring 1987, pp. www.gia.edu/gemsandgemology.] was then inserted into each of the crys- Wendi M. Mayerson tals, conforming to the cylindrical shape of the drilled holes. The holes Figure 17. Although the asterism were then filled with a resin or similar in this rock crystal quartz cabo- compound (figure 15), and the speci- chon is natural, the color is Figure 18. A chip on the bottom of men was reassembled. We surmise that caused by a blue coating on the the cabochon in figure 17 reveals once the paper was saturated by the back, probably to help it imitate colorless quartz underneath the resin, it became transparent, leaving star sapphire. blue coating. Magnified 30×. only the wording, in black, visible from the outside of the crystal (figure 16). Although this is not the only possible scenario, it seems the most likely. One of our staff members at the time, Maha Calderon, was able to read most of the two inscriptions, the first of which she translated as, “To the people, guidance, and wisdom to the believers.” Only part of the sec- ond inscription was legible because of inclusions in the emerald. SFM
60 LAB NOTES GEMS & GEMOLOGY SPRING 2006 nated turquoises have lower refractive indices that may fall within this range. The samples were all backed with a black material, so a meaningful specif- ic gravity could not be obtained. Our standard laboratory procedure is to test all turquoise for polymer impregnation using infrared spec- troscopy. The IR spectrum of this material, however, did not resemble that of turquoise at all. This effectively eliminated turquoise as a possible identification, so the next step was to obtain a Raman spectrum. The results showed a very close, but not exact,
match to variscite (AlPO4 • 2H2O). Variscite is a mineral in the variscite group that forms a complete solid solu- ± tion with strengite (Fe3 PO4 • 2H2O). The final test was X-ray diffraction Figure 19. This 25.35 × 17.70 × 5.75 mm cabochon was one of several samples (XRD) analysis. After comparing the submitted to the laboratory that at first appeared to be spiderweb turquoise, sample to known patterns, we deter- but proved to be variscite. Its resemblance to true spiderweb turquoise from mined that the material was in fact the Lander Blue turquoise mine in Nevada (inset) is quite striking. variscite. Minor variations in the Raman spectrum and the XRD pat- tern were probably due to variations within the variscite series. This was the first time that a sample of variscite VARISCITE, Resembling Turquoise Edelstein mit der Farbe des Himmels” with an appearance this close to Several cabochons of a mottled green- [Turquoise: The Jewel with the Color turquoise was seen in our lab. Even blue material in black matrix (figure of the Sky], extraLapis No. 16, our most experienced gemologists 19), represented as turquoise from Christian Weise, Munich, 1999, pp. would not have suspected this materi- Lander, Nevada, were recently sub- 34–41). al to be variscite at first glance. mitted to the West Coast laboratory The submitted material strongly Eric Fritz and Kimberly Rockwell for identification. The now-inactive resembled this unusually textured Lander Blue turquoise mine was turquoise, but the color was less satu- noted for small pockets of nodular rated than we would expect from this turquoise with black matrix (figure locality. Microscopic examination PHOTO CREDITS 19, inset) that was called “spiderweb” revealed a structure and texture that Elizabeth Schrader—1; Shane F. McClure— turquoise. The deposit has been were not typical of turquoise, but 2 (left), 15 and 16; Shane Elen—2 (center referred to as a “hat mine” because could not rule it out given the many and right); Maha Calderon—3, 5, 13, and the pockets were small enough to be deposits and treatments possible for 14; Christopher M. Breeding—4 and 8; covered by a hat. The deposit was dis- this gem material. The refractive Wuyi Wang—6 and 7; Jessica Arditi—9 covered in 1973, and during its rela- indices of the 20.16 ct piece we tested and 17; Kyaw Soe Moe—10 and 12; Wendi tively short lifespan only 104 lbs. (47 were 1.570–1.590, which are lower Mayerson—18; Don Mengason—19 and 19 (inset). kg) of spiderweb turquoise was mined than the published values for tur- (A. Ahmed et al., “Türkis: der quoise. Again, however, many impreg-
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LAB NOTES GEMS & GEMOLOGY SPRING 2006 61