corundum, treatments.6, gems

A beautiful orangy yellow oval mixed-cut stone weighing 7.60 ct was submitted to the Santa Monica laboratory for identification. The refractive index, birefringence, and optic figure proved that the stone is sapphire. Microscopic examina-tion revealed natural inclusions as well as the strain discs, very fine dot-like silk," and round cotton-like inclusions that are indicative of heat treatment. Exposure to short-waveultravio-let radiation revealed three zones of chalky blue fluorescence close to the girdle, another sign of heat treat-ment. When the stone was immersed in methylene iodide, some interest-ing structural characteristics be-came visible. In addition to the straight angular yellow color zoning alternating with near-colorless areas, which is characteristic of natural origin, three straight blue zones close to the girdle (coinciding with the areas of chalky blue fluores cence] were seen. Figure 10 showo these blue areas, which could be the result of the heat treatment."