An Assembled ‘Emerald’ Rough
New gem discoveries invariably generate considerable interest within the industry. Recently, a specimen was submitted to Guild Gem Laboratories in Shenzhen as a purported rough emerald specimen from a newly discovered deposit in Zambia (Figure 1). Initial macroscopic examination revealed an appearance consistent with Zambian emerald rough, displaying transparent green ‘crystals’ within a matrix of a greyish brown mica-like mineral (Figure 2), accompanied by some areas with an iron-stained appearance. As is well established in the literature, emerald crystals from Zambian deposits are typically hosted by phlogopite schist (e.g. Zwaan et al. 2005). However, detailed microscopic examination combined with spectroscopic and chemical analysis revealed the deceptive nature of this specimen.
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| Figure 1: This assembled ‘emerald’ rough (65.92 × 35.80 × 26.47 mm) was purportedly from a new emerald deposit in Zambia, but it proved to be a rather convincing imitation. Photo by Siqi Luo. |
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| Figure 2: Most of the surface of the specimen is covered with a micaceous material, which was identified as phlogopite by Raman analysis. Photomicrograph by Ziyun Zhang; image width 6.6 mm. |
Viewed with the microscope, two types of green ‘crystals’ became evident: those that were clean inside, through which abundant gas bubbles could be seen trapped in a layer of underlying resin-like material (Figure 3a), and those containing naturallooking fluid inclusions (Figure 3b). All component interfaces in the specimen were extensively permeated with the resin-like material, which had a low Mohs hardness and could be easily scratched by a fingernail. In some areas this substance was colourless and in others it appeared green.
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| Figure 3: Microscopic features of the green components of the specimen include (a) a large quantity of gas bubbles trapped within the resin beneath a piece of green glass, and (b) fluid inclusions in a piece of quartz. Photomicrographs by Ziyun Zhang; image widths (a) 2.0 mm and (b) 0.8 mm. | |
Raman spectroscopy showed that the green ‘crystals’ indeed consisted of two materials: glass exhibiting a diagnostic broad peak at 1090 cm–1, and quartz identified by its characteristic vibrational modes at 465 and 207 cm–1, consistent with quartz reference sample R050125 in the RRUFF database. The high Cr content (1,121 ppmw) within the glass component, as revealed by EDXRF spectroscopy, produced the green colouration. The green colour of the quartz was due to the underlying green resin-like substance.
The greyish brown micaceous matrix material was identified as phlogopite, with characteristic Raman peaks at 676 and 189 cm–1, consistent with phlogopite reference sample R050485 in the RRUFF database. The brownish red areas of the specimen did not yield a usable Raman signal due to strong fluorescence, but analyses with Fourier-transform infrared and EDXRF spectroscopy showed they consisted of Fe-bearing minerals.
X-ray imaging using a Seamark X6600 X-ray inspection system also provided definitive evidence of the artificial assemblage, revealing resin-dominated zones constituting nearly 40% of the specimen’s volume and forming interconnected networks that mechanically bonded all the components together (Figure 4).
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| Figure 4: An X-ray image of the approximately 66-mm-long specimen reveals the large amount of resin present, which is seen here as light grey areas, mainly in the centre. The bright white areas consist mostly of glass. Image by Ziyun Zhang. |
This specimen proved deceptive on multiple levels: the phlogopite layer convincingly simulated the schist host rock typical of Zambian deposits, and the pieces of green glass and quartz provided an appropriate vitreous lustre and colour saturation for imitating emerald. This case underscores an evolving threat in gem imitations, and the gemmological community must remain vigilant.
Xueying Sun, Yujie Gao (peter.gao@guildgemlab.com), and Ziyun Zhang
Guild Gem Laboratories, Shenzhen, China
Reference
Zwaan, J.C., Seifert, A.V., Vrána, S., Laurs, B.M., Anckar, B., Simmons, W.B., Falster, A.U., Lustenhouwer, W.J. et al. 2005. Emeralds from the Kafubu area, Zambia. Gems & Gemology, 41(2), 116–148, https://doi.org/10.5741/gems.41.2.116.
