Micro-World Gems & Gemology, Spring 2019, Vol. 55, No. 1

Sapphire Inclusion with Rutile “Silk” in a Burmese Star Sapphire

A guest crystal in the star sapphire viewed under cross-polarized light (left) and fiber-optic light (right).
A guest crystal located at the back of the star sapphire stands out under cross-polarized illumination, exhibiting concentric rings of interference colors when viewed along its optic axis (left). Examination with fiber-optic light revealed a group of needle-like rutile inclusions oriented along the basal plane of the sapphire inclusion (right). Photomicrographs by Xiaodan Jia; field of view 3.83 mm.

GIA’s Hong Kong laboratory recently examined a remarkable sapphire inclusion inside a Burmese star sapphire. Possessing the same refractive index as its host, the sapphire guest displays extremely low relief and is nearly invisible under transmitted light. Nevertheless, its outline became distinctive under cross-polarized illumination, showing strong interference colors (see above, left). Closer examination using fiber-optic illumination revealed a group of oriented rutile “silk” in this sapphire inclusion (see above, right). Although exsolved rutile needles are a common inclusion in Burmese sapphire, it is interesting to see two sets of dense silk exsolved from both the star sapphire host and a protogenetic sapphire inclusion, each aligned with the basal plane of its own host.

Xiaodan Jia is a senior staff gemologist, and Mei Mei Sit is supervisor of colored stones identification, at GIA in Hong Kong.