Gem News International Gems & Gemology, Fall 2015, Vol. 51, No. 3

Coated Rock Crystal Imitation of Ruby

Rock crystal coated with brown skin.
Figure 1. This coated rock crystal imitation of ruby has a brown skin. Photo by Nazar Ahmed Ambalathveettil, Dubai Central Laboratory.

Recently the Dubai Central Laboratory received for identification a rough stone weighing 616.93 g and measuring approximately 114.3 × 65.8 × 53.0 mm (figure 1). Most of it was covered by a brown skin, while other parts were transparent. Viewed through one of the transparent areas, the stone showed a red color. Under oblique light, the stone appeared dark red, with some areas that were colorless (figure 2).

Rock appears dark red under transmitted light.
Figure 2. The rock crystal shows dark red under transmitted light to imitate ruby. Photo by Nazar Ahmed Ambalathveettil, Dubai Central Laboratory.

Microscopic examination with transmitted light revealed negative crystals, fingerprints, and two-phase inclusions. Observation of the transparent and opaque areas on the surface showed red, green, and blue areas of coating that could be removed using sharp needles. These coated areas gave the stone a purplish red color overall, but some transparent areas appeared colorless under transmitted light and no coating was observed there. The stone’s specific gravity (SG) was 2.60. The coated area gave a patchy chalky blue and purple reaction under long-wave UV and was inert to short-wave UV. SG and inclusions indicated a rock crystal; this was confirmed by Raman spectroscopy.

This was the first time the Dubai Central Laboratory had identified such a large coated rough stone imitating ruby.

Nazar Ahmed Ambalathveettil is a principal gemstone analyst, and Mohamed Karam is a gemstone analyst, at the Gemstone Unit of the Dubai Central Laboratory in the United Arab Emirates.