Spodumene (LiAlSi2O6) is a clinopyroxene; its name is derived from the Greek spodumenos ("burnt to ash"), in reference to the gray/ash-colored, non-gem material that has been mined commercially as a source of lithium ore (J. Sinkankas, Mineralogy, Van Nostrand Reinhold, New York, 1964, pp. 494–497). Common colors for gem-quality spodumene include pink-to-"lilac" (kunzite), pale greenish yellow (triphane), pale violet-blue, pale green, and colorless. In addition, a distinctive chromium-bearing "emerald"-green spodumene (hiddenite) is known principally from Hiddenite, North Carolina (e.g., M. A. Wise and A. J. Anderson, "The emerald- and spodumene-bearing quartz veins of the Rist emerald mine, Hiddenite, North Carolina," Canadian Mineralogist, Vol. 44, 2006, pp. 1529–1541).
In late 2006, Dudley Blauwet and Herb Obodda informed us about a new find of a distinctly green spodumene in Afghanistan. Mr. Blauwet first encountered this material in June 2006 while on a buying trip to Peshawar, Pakistan. At that time, local traders did not know the identity of the gem rough. It was typically available as small cleavage fragments, quite unlike the large well-formed crystals of spodumene that are coveted from Afghanistan (e.g., L. Natkaniec-Nowak, "Spodumenes from Nuristan, Afghanistan," Australian Gemmologist, Vol. 23, 2007, pp. 51–57). Farooq Hashmi, who visited Peshawar in June 2007, saw a 30 kg mixed-quality parcel of the green spodumene, and another 2 kg lot of higher-quality material; most was pale colored but some pieces were "emerald" green and appeared pink with the Chelsea filter. The main supplier of the spodumene told him that it came from "Waigal," which is several hours’ walk from the village of Wadigram in the Nuristan area. It was reportedly found at a small digging in a single pegmatite in an area where other pegmatites are mined for blue tourmaline and kunzite.
Mr. Blauwet and Mr. Obodda loaned or donated to GIA several pieces of rough and a 1.45 ct faceted sample of the green spodumene (e.g., figures 1 and 2). Examination of the cut stone gave the following properties: color—light green, with no visible pleochroism; RI—1.662–1.678; birefringence 0.016; hydrostatic SG—3.25; fluorescence—inert to long- and short-wave UV radiation; Chelsea filter—weak positive reaction (grayish pink); and no absorption lines visible with the desk-model spectroscope. These properties are consistent with those reported for spodumene by J. W. Anthony et al. (Handbook of Mineralogy, Vol. 2, Mineral Data Publishing, Tucson, AZ, 1995, p. 747), except that the SG is slightly higher than published values (3.03–3.23). Microscopic examination revealed multiple fractures and one long needle-like inclusion.
Some of the rough samples (e.g., figure 1) showed a noticeable gradation from green to yellow-green. Green in spodumene can also be produced by artificial irradiation; however, the induced color fades when exposed to sunlight for a few hours (G. R. Rossman, "Color in gems: The new technologies," Summer 1981 Gems & Gemology, pp. 60–71; K. Nassau, "Treatments used on spodumene: Kunzite and hiddenite," Colored Stone, Vol. 1, No. 7, 1988, pp. 16–17). To test the color stability of this Afghan spodumene, the rough sample was divided into two pieces, the larger portion of which was left in the Southern California sun for three weeks. When compared to the control portion, it showed no indication of fading (again, see figure 1).
Further testing was conducted to determine the cause of color. EDXRF spectroscopy of the cut stone showed traces of the chromophoric elements Mn, Fe, Cr, and V. Electron-microprobe analyses of a rough sample donated to the University of New Orleans by Mr. Blauwet showed an average of 0.13 wt.% MnO and 0.02 wt.% FeO (all iron expressed as FeO; average of 6 analyses); Cr and V were below the detection limits of the instrument. (By comparison, Wise and Anderson [2006] reported up to 0.14 wt.% Cr2O3 and 0.08 wt.% V2O3 in spodumene from Hiddenite, North Carolina.) LA-ICP-MS analyses at GIA of another rough sample showed systematic variations in Cr and V, with the highest amounts measured in the green portions of the sample; there were no distinct differences in Fe and Mn content according to color. The composition of the yellow-green portion was similar to data reported for a green-yellow spodumene from Afghanistan by Natkaniec-Nowak (2007).
The UV-Vis absorption spectrum of the sample in figure 2 showed that its coloration was caused by a transmission window at ~420–600 nm, which is characteristic of Cr- ± V-bearing spodumene (E. W. Claffy, "Composition, tenebrescence and luminescence of spodumene minerals," American Mineralogist, Vol. 38, 1953, pp. 919–931). The greener portion of the sample had greater absorbance in the 550–700 nm region, which in spodumene is attributed to Cr and/or V (R. G. Burns, Mineralogical Applications of Crystal Field Theory, 2nd ed., Cambridge University Press, Cambridge, UK, 1993, pp. 188–189).
There may be some debate as to whether the Afghan samples could be properly referred to as hiddenite. A survey of the literature showed that there is no consistent definition for this variety of spodumene. Although this term is typically used to refer to yellow-green to green Cr-bearing spodumene, it is unclear if the saturation of the green color is important to the definition. To our knowledge, Cr-bearing spodumene is now known from Brazil, India, Siberia, and Afghanistan, in addition to the original area near Hiddenite, North Carolina.
Karen M. Chadwick (karen.chadwick@gia.edu) and Andy H. Shen
GIA Laboratory, Carlsbad
Brendan M. Laurs
William B. (Skip) Simmons and Alexander U. Falster
University of New Orleans, Louisiana
