“Boomerang” Inclusion in a Rough Topaz

Shu-Hong Lin, Tsung-Ying Yang, Kai-Yun Huang, and Yu-Shan Chou

A 21.46 ct colorless rough topaz was recently submitted to Taiwan Union Lab of Gem Research (TULAB) for identification service. Microscopic observation showed a few prismatic brown inclusions with submetallic luster. One of the inclusions was a unique twinned crystal composed of two prismatic crystals forming a 120° intersection angle. With its shape and backdrop, the twinned crystal resembled a boomerang flying across the sky (see above). This inclusion was later confirmed to be tantalite-(Mn), based on Raman spectroscopy and comparison with the RRUFF database. Polarized light and reflected illumination were adopted to reduce doubling and obtain clearer photomicrographs, and the images were processed to extend depth of field.