Purplish Pink Spinel from Tajikistan: Before and After Cutting
In December 2007, Pakistan-based client Syed Iftikhar Hussain submitted a parcel of spinel rough reportedly from Tajikistan (figure 9, left). These 84 samples, the largest weighing 48.5 g, exhibited varying saturations of purplish pink color. Little has been written on the properties of Tajik spinel (see, e.g., J. I. Koivula and R. C. Kammerling, “Examination of a gem spinel crystal from the Pamir Mountains,” Zeitschrift der Deutschen Gemmologischen Gesellschaft, Vol. 38, 1989, pp. 85–88), so in November 2008 the Bangkok laboratory was fortunate to have an opportunity to briefly examine seven stones that the client had faceted from this parcel (figure 9, right).
Most of the original rough consisted of broken pieces, and only a few showed the octahedral crystal forms typical of spinel. We could not perform accurate RI measurements because of the lack of flat surfaces, so we had to rely on other tests. The hydrostatic SG measurements, spectra seen with a handheld spectroscope, polariscope reactions, and UV fluorescence were consistent with spinel. These observations were further substantiated by PL spectroscopy (514 nm laser excitation at room temperature) on the largest piece, which proved it was natural spinel. The most prominent inclusions seen in the samples were euhedral crystals, needles, and crystals with white particulate trails forming “comet tails” (figure 10).
After the rough was cut, we obtained standard gemological properties for the seven faceted stones. The results were fairly consistent: RI— 1.712–1.713, SG—3.59–3.62, strong red fluorescence to long-wave UV radiation and weak red to weak-tomoderate orange (some with a chalky greenish cast) fluorescence to shortwave UV, and a characteristic “organ pipe” spectrum (with some general absorption in the orange/yellow and part of the green region) seen with the spectroscope. While the refractive indices were almost identical to that of the crystal detailed by Koivula and Kammerling (and a Tajik spinel reported in the Spring 1989 Lab Notes, pp. 39–40), the SGs varied slightly.
Since the cleanest pieces of rough were likely selected for faceting, it was no surprise that six of the cut stones showed few inclusions. The 11.96 ct pear shape hosted the most internal features, which consisted of a plane of octahedral negative crystals and some euhedral crystals (figure 11). Tiny negative crystals were only faintly visible in one other stone. Unfortunately, there was no time to identify inclusions in either the rough or cut spinels with Raman spectroscopy. The PL spectrum of the pear-shaped stone closely matched that of the rough sample.
Nicholas Sturman has over 26 years of detailed experience in the examination of pearls. He obtained his FGA and DGA qualifications in the UK prior to joining the world renowned Gem Testing Laboratory of Great Britain, when it existed, and continued with 16 years studying pearls in the Kingdom of Bahrain where he was employed as the gemological advisor to the Bahrain Government’s Gem and Pearl Testing Laboratory. Nick specializes in the separation of natural pearls from all types of cultured pearls using Real-Time Microradiography and X-ray Computed Microtomography (CT) units in-house at the GIA Bangkok laboratory. He also oversees the final work on jobs before they are completed and works with his team to complete client work quickly and accurately. As well as writing contributions to various gemological publications he has also given presentations in Thailand, Singapore, Hong Kong, Japan, The United Kingdom, France, Switzerland and various countries within the Middle East. Nick also assists with teaching and educational seminars when required, and has co-authored two books “Kunooz Al-Bahrain” and “Splendour and Science of Pearls”. Nick was also the joint winner of the 2010 Dr. Edward J. Gubelin Most Valuable Article Award, as voted by Gems & Gemology readers.
Ken Scarratt—9 left, 10; Suchada Kittayachaiwattana—9 right; Nicholas Sturman—11.