Micro-World Gems & Gemology, Summer 2024, Vol. 60, No. 2

Quartz with Sphalerite

John I. Koivula, Nathan Renfro, and Maxwell Hain

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Figure 1. This 182.19 ct quartz cabochon hosts a brownish orange phantom with a netlike structural form. Photo by Adriana Robinson.
 
Figure 1. This 182.19 ct quartz cabochon hosts a brownish orange phantom with a netlike structural form. Photo by Adriana Robinson.

The Taolin mine in Linxiang County, Hunan Province, China, is known to produce fine specimens of gemmy, brownish orange sphalerite, together with quartz. We recently examined a transparent and colorless rectangular freeform double cabochon (figure 1) fashioned from a Taolin quartz crystal. The cabochon weighed 182.19 ct and measured 44.70 × 29.81 × 15.76 mm.

Figure 2. A network of rounded and stretched crystals, islands, and puddles of sphalerite that look as if they were once in a liquid state. Photomicrograph by Nathan Renfro; field of view 9.92 mm.
 
Figure 2. A network of rounded and stretched crystals, islands, and puddles of sphalerite that look as if they were once in a liquid state. Photomicrograph by Nathan Renfro; field of view 9.92 mm.

Interestingly, this specimen played host to a phantom of transparent brownish orange inclusions that formed as a network of rounded and stretched crystals, islands, and puddles. The appearance of these features suggested they were once in a liquid state (figure 2) and were originally deposited as a viscous liquid in the quartz.

Several parts of the phantom were near the surface of the host quartz, and some had been polished through and exposed at the surface. This made the inclusions ideal for Raman analysis, which proved that the phantom was made up of individual islands and tendrils of the mineral sphalerite.

John I. Koivula is analytical microscopist, Nathan Renfro is senior manager of colored stone identification, and Maxwell Hain is a staff gemologist, at GIA in Carlsbad, California.