Metal Sulfide Crystal in a Sapphire

Muzdareefah Thudsanapbunya

The author recently examined a faceted sapphire from Sri Lanka. Gemological analysis confirmed that it was unheated. The sample contained a crystal that, when examined under the microscope using darkfield illumination and oblique fiber-optic illumination, exhibited a highly reflective surface. The observations of the metallic luster and rounded appearance (see above) suggested that this inclusion was most likely an iron sulfide.

Iron sulfides are found as opaque mineral inclusions with metallic luster in corundum. The iron sulfides usually seen in corundum are pyrite (FeS₂) and pyrrhotite (Fe_1-xS) (E.J. Gübelin and J.I. Koivula, Photoatlas of Inclusions in Gemstones, Vol. 3, Opinio Publishers, Basel, Switzerland, 2008, p. 285). Also present was a partially healed fracture, or fingerprint, next to this crystal, which made for an interesting inclusion scene.