Rubies and sapphires are found worldwide. See corundum treatments for more information. Lead glass filling: Fills fractures, improves clarity.

CORUNDUM: Sapphire-Star sapphire, Sri Lanka (31.87). Very rarely there are two distinct sets of needles oriented according to the first and second order prisms of the corundum (30° apart), resulting in a strong, 12-rayed star.įor more information on corundum inclusions, see Identifying Origins of Rubies and Sapphires. When such material is cut into a cabochon the sheen is concentrated along the top of the stone into three white lines crossing at 120° angles, creating a six-rayed star. The rutile needles orient themselves according to the hexagonal symmetry of the corundum, and reflections from these needles provide a chatoyancy. Star corundum gemstones show asterism, or a 'star effect.' This phenomenon is created by the inclusion of rutile needles within the host corundum crystal.

Among sapphires the green gems are more iron-rich, have higher indices.ĬORUNDUM: Star ruby, Sri Lanka (2.75), Burma (2.6, 0.62), India (8.4). Synthetics: See Identifying Inclusions and Synthetic Gemstones and Their Identification.Ĭharacteristics of Corundum from Various Localities

Sapphire and ruby gemstones