corundum, inclusions.5, Umba sapphires, gems

New evidence of treatment in Umba sapphires. Any evidence that provides absolute proof that a sapphire has or has not been heat treated is always of value to gemologists. A recent investigation done by one of the Gem News editors (JIK), which was published in the Journal of Gemmology (Vol. 20, No. 7, 1987), showed just such evidence in the form of colored halos surrounding solid mineral inclusions in sapphires from Sri Lanka and Montana. The halos result from the heat-induced theft, by the sapphire host, of color-causing ions from the mineral inclusions. After reading the above-mentioned article, Dr. Henry A. Hänni of the University of Basel and the Swiss Foundation for the Research of Gemstones contacted Gem News and reported his discovery of similar internal diffusion halos surrounding tiny mineral inclusions in blue sapphire from the Umba River region in Tanzania, East Africa (figure 6). Dr. Hänni’s observation provides positive evidence that at least some of the sapphires from this locality are being heat treated.