gems, corundum, synthetic corundum.7, Kashan, treatments.6

From G&G: At the Gem Testing Laboratory in Jaipur, India, a 4.63 ct synthetic star sapphire displaying hexagonal zoning was initially mistaken for a natural sapphire with a diffusion-induced star due to its wavy star rays and “silk” inclusions. The cabochon fluoresced chalky blue under short-wave UV radiation and exhibited chromium lines in a desk-model spectroscope. Upon magnification and immersion, a hexagonal zone was visible in the core, surrounded by a wavy stress pattern, with fine needles in three directions creating the star effect. However, when viewed from the back, numerous tiny whitish pinpoints, likely gas bubbles, were arranged in curved clouds, and immersion with diffused illumination revealed curved color bands—diagnostic of a flame-fusion synthetic origin. The cause of the hexagonal zoning remains uncertain, but it may result from a crystallographically oriented concentration of silk in the core. Higher magnification with a strong fiber-optic light revealed a denser concentration of needles in the core compared to the surrounding area. This was the first documented case of both hexagonal zoning and curved color bands appearing together in a single specimen, highlighting the importance of thorough gemological analysis to avoid misidentification, especially in closed-back settings where key diagnostic features may be obscured.