corundum, Sri Lanka.12, inclusions.5, gems

Duyk describes an unusual 51 ct sapphire cabochon, apparently from Sri Lanka, containing two conspicuous internal cavities with well-developed crystalline outlines. He examines the morphology and optical appearance of these voids and discusses their relationship to the host sapphire, illustrating the features with nine photographs. The observations show that apparently empty, crystallographically shaped cavities can occur as internal features in natural sapphire and may provide useful evidence concerning the stone’s growth history.