Micro-World Gems & Gemology, Fall 2015, Vol. 51, No. 3

Molybdenite in Topaz

Brazilian colorless topaz with molybdenite inclusions.
Figure 1. This 4.71 ct Brazilian colorless topaz hosts a cluster of hexagonal molybdenite crystals. Photo by Kevin Schumacher.

A photogenic cluster of hexagonal molybdenite crystals (MoS2) was recently discovered in a 4.71 ct transparent colorless hexagonal step-cut topaz (figure 1). The topaz host was identified using traditional gemological testing, and the molybdenite cluster (figure 2) was identified through its metallic luster, morphology, and the presence of molybdenum, which was detected using focused EDXRF analysis.

Molybdenite crystal inclusions in topaz.
Figure 2. It was a surprise to discover molybdenite crystal inclusions in topaz. Shadowed lighting reveals iridescence and surface details on the cluster, which measures 2.82 mm in length. Photomicrograph by Nathan Renfro.

This gem, which came from Luciana Barbosa of the Gemological Center in Ashville, North Carolina, is from Seridó, Rio Grande do Norte, Brazil. We have never seen this inclusion-host association before, and it is not previously recorded in the literature. This elegant gem is a perfect micromount of molybdenite in a faceted showcase.

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