Gem News International Gems & Gemology, Summer 2015, Vol. 51, No. 2

Cat’s-Eye Calcite from Pakistan

A calcite cabochon showing a cat’s eye.
Figure 1. This 57.60 ct calcite from Pakistan shows a cat’s-eye. Photo by Jaroslav Hyršl.
Cat’s-eye calcites have been sold at auctions and gem shows for some years, but a gemological description of the material has not been published. Low-quality cat’s-eye calcites do exist, such as blue calcites from Mogok, Myanmar, but their chatoyancy is weak. It was very surprising, therefore, to see sharp chatoyancy on the beautiful calcite cabochon in figure 1.

The stone, purchased during the Tucson shows in February 2015, came from the Baluchistan province of Pakistan. It weighed 57.60 ct and measured 25.0 × 24.6 × 12.3 mm. It was light green and translucent, without eye-visible inclusions. The spot RI ranged from 1.48 to 1.66, and when rotated the cabochon showed a strong “blink” typical for carbonates. This is significant because the stone resembled chrysoprase; without the rotation, the measured RI in a given position might also approximate that of chrysoprase. There were no lines in the visible spectrum, the stone was inert under UV light, and its specific gravity was 2.72. Viewed in the polariscope, it remained bright, indicating a doubly refractive aggregate. Strong banding (figure 2) was present in the direction of chatoyancy, but the bands were inclined at about 20° angles. The bands were approximately 0.7 mm thick.

Banding in the chatoyant calcite cabochon.
Figure 2. Banding in chatoyant calcite from Pakistan, as seen through the bottom of the cabochon. Photo by Jaroslav Hyršl.
Only at 40× magnification did the cause of the chatoyancy become apparent. Numerous tiny needles perpendicular to the chatoyancy were likely evidence of a columnar to needle-like texture. Other than the chatoyancy, this specimen is similar in appearance to the green and orangy yellow calcites from Pakistan that were described in the Fall 2012 GNI section (pp. 217–218). It is the opinion of both the seller and the author that this calcite is from the same locality.

Jaroslav Hyršl is a mineralogist and author in Prague.