Micro-World Gems & Gemology, Summer 2016, Vol. 52, No. 2

Metal Sulfide in Pyrope

Pyrope garnet with metal sulfide inclusion
Figure 1. The prominent sulfide inclusion in this 2.02 ct pyrope is clearly visible under the table facet. Photo by Kevin Schumacher.

The 2.02 ct “inclusion gem” shown in figure 1 is not only spectacular to inclusion enthusiasts, but also a scientific mystery. This vanadium- and chromium-bearing pyrope was cut from one of the samples featured in G&G’s Winter 2015 issue (Z. Sun et al., “Vanadium- and chromium-bearing pink pyrope garnet: Characterization and quantitative colorimetric analysis,” pp. 348–369). The stone was faceted by Jason Doubrava (Poway, California) to display a relatively large, euhedral sulfide crystal inclusion. Sulfide crystals were observed in several of the samples in the 2015 study; the exact nature of the inclusions could not be determined by Raman analysis, but all displayed a metallic luster in surface-reflected light. Magnification also revealed a cloud of minute acicular inclusions resembling rutile surrounding the crystal (figure 2). Along with the elements expected for pyrope, such as Si, Al, Mg, Mn, and Fe, energy-dispersive X-ray fluorescence (EDXRF) analysis detected peaks for sulfur and rhodium. While sulfur would be expected in a metal sulfide, the rhodium peak is a mystery. Rhodium sulfide does exist, but explaining the presence of rhodium in this garnet would require destructive testing. In this case beauty trumps science, because this gem is truly a wonderful addition to the collection of this inclusionist and will thus remain a gemological curiosity.

Inclusions surround the sulfide.
Figure 2. A cloud of extremely fine acicular inclusions in the pyrope surrounds the sulfide when viewed under the microscope with diffuse reflected light. Photomicrograph by Nathan Renfro; field of view 5.41 mm.

John I. Koivula is the analytical microscopist at GIA in Carlsbad, California.