“Olive” green and “chrome” green diopside reportedly from Badakhshan, Afghanistan, were brought to our attention by Farooq Hashmi (Intimate Gems, Jamaica, New York), who obtained the gem-quality rough while on a buying trip to Peshawar in January 2006. The two diopside varieties come from separate deposits that have been worked on an irregular basis for at least two years.
Mr. Hashmi obtained 3–4 kg of the “olive” green diopside from various parcels that totaled about 15 kg. The cobbed rough typically contained abundant inclusions, and the limited quantities of clean transparent pieces mostly weighed <3 grams each. The “chrome” diopside was available in larger quantities (i.e., parcels weighing up to 30–40 kg), and was reportedly cobbed from pods of material measuring up to several centimeters in diameter that were hosted by black mica schist. Extracting the gem-quality pieces was challenging due to the cleavage of the diopside.
Mr. Hashmi had a few stones faceted from each diopside variety, and loaned/donated them to GIA for examination by one of us (EPQ). Gemological testing of three “olive” diopsides (1.33–2.75 ct; figure 1) showed the following properties: color—medium to medium-dark yellow-green; pleochroism—very weak, brownish yellow and gray-green; R.I.—nα=1.674–1.675 and nγ=1.701–1.703; birefringence—0.027–0.028; and hydrostatic S.G.—3.29–3.30. These properties are consistent with those reported for diopside by W. A. Deer et al. (An Introduction to Rockforming Minerals, 2nd ed., Longman Scientific and Technical, Essex, England, 1992, pp. 170–176). There was no Chelsea filter reaction, and the stones were inert to both long- and short-wave UV radiation. Absorption features at approximately 450, 505, and 550 nm were visible with the desk-model spectroscope. Microscopic observation revealed moderate doubling of the facet junctions, small transparent low-relief doubly refractive crystals and needles in stringers and planes, and small dark crystals. The stones also contained clouds and stringers of minute particles (which appeared dark in diffused light but white or gray in darkfield illumination); some of the clouds were planar. One of the stones displayed twinning, while another sample had partially healed fractures. EDXRF spectroscopy of two of the samples indicated the presence of major amounts of Si, Ca, and Mg; minor Fe; traces of Mn and Sr; and possibly Y and Zn.
Gemological testing of four faceted “chrome” diopsides (0.57–0.77 ct; figure 2) showed the following properties: color—medium-dark to dark green; diaphaneity—transparent; pleochroism—moderate, brownish yellow and green; R.I.—nα=1.678 and nγ=1.705; birefringence—0.027; S.G.—3.30–3.32; Chelsea filter reaction—none; and fluorescence—inert to both long- and short-wave UV radiation. Again, these properties were consistent with those of diopside reported by Deer et al. (1992). Absorption features at approximately 505, 550, 640, 660, and 690 nm were visible with the desk-model spectroscope; the lines in the red end of the spectrum are consistent with the presence of Cr, while the other features are probably due to iron. Microscopic examination revealed moderate doubling of the facet junctions, small low-relief doubly refractive transparent crystals and needles, and small dark crystals. The stones also contained clouds and stringers of particles and needles (which appeared dark in diffused light but white or gray in darkfield illumination); some of the clouds were planar, and the stringers had a wavy stair step–like configuration. Two of the stones had partially healed fractures and two contained larger, doubly refractive, low-relief acicular crystals. EDXRF spectroscopy of three of the samples indicated the presence of major amounts of Si, Ca, and Mg; minor Fe; traces of Cr, Ti, Mn, and Sr; and possibly V. The absorption spectra and the detection of Cr in these samples by EDXRF indicate that the intense green color of this diopside is likely due to chromium.
Elizabeth P. Quinn
GIA Laboratory
Brendan M. Laurs
