gems, spinel, Sri Lanka, sillimanite inclusions

A bluish-violet spinel from Sri Lanka with oriented inclusions was examined using microscopy, X-ray single-crystal diffraction, and electron microprobe analysis. The specimen displays four sets of lath-like, double-refracting crystal inclusions aligned parallel to the threefold axes of the host spinel. The inclusions are identified as one of the Al₂SiO₅ polymorphs, most likely sillimanite. The study also includes a general literature review on oriented inclusions and asterism in spinel.