corundum, treatments.6, India.12, gems

Sixteen red cabochons purchased from a German dealer as natural star rubies were identified as dyed natural star corundum. The specimens measured approximately 7–12 mm, displayed intense red body color and sharp six-rayed stars, and, according to information supplied by the seller, were probably imported from India. Standard gemological tests established that the material was corundum. Microscopic examination revealed growth zoning associated with prism faces and hexagonal dipyramids, natural inclusions, and, in some specimens, parting parallel to the positive rhombohedron, supporting a natural origin. In several cabochons, the star rays ran perpendicular to traces of the observed growth planes, an orientation described as typical of Indian star corundum containing oriented rutile needles. Differences in the concentration of these needles between growth sectors produced variations in the milky-white appearance of the stones under reflected light. The red coloration, however, was concentrated unevenly within fissures and cracks traversing the crystals, demonstrating that the apparent ruby color was artificial. Neither the corundum nor the coloring material in the fissures fluoresced under long-wave or short-wave ultraviolet radiation. Immersion of one specimen in acetone removed part of its red color, and red spots subsequently appeared on the stone’s wrapping material, providing further evidence of dye treatment. The absence of fluorescence distinguished these samples from previously reported dyed corundum beads and faceted stones, in which the coloring agent produced strong yellow-orange fluorescence under long-wave ultraviolet radiation, and indicated the use of a different dye. The Mysore–Karnataka region of southern India is suggested as a possible source of the starting material because it had supplied substantial quantities of pale-colored star corundum and dyed material from that area had previously been reported. This geographic attribution remains tentative. The study demonstrates that natural inclusions and genuine rutile-induced asterism can coexist with artificially introduced red coloration. Identification depends principally on recognizing the irregular concentration of dye in fractures, a feature visible microscopically and sometimes with a hand lens.