Many gemstones are phenomenal gems, meaning they possess a distinct optical quality that gives rise to one of several phenomena of light.
One such phenomenon is the asterism, or star-like pattern, which appears as rays across the domed surface of a given gemstone. Asterisms can occur in many types of gemstones including sapphire, ruby, quartz, and garnet. Inclusions and geometrically aligned crystal layers give rise to this interesting and beautiful play of light.
Another type of phenomenal gems exhibit what is referred to as chatoyancy, or cat’s eye. Because of the fibrous structure of the gem or inclusions, this optical reflectance can be observed in gems like quartz, chrysoberyl, tourmaline, and others.
Adularescence, another phenomenal characteristic, is a silver glow that occurs in gems like moonstone, while iridescence, as in ammolite, is similar to a rainbow.
Phenomenal gems are intriguing to view and are unmatched in beauty in the geological world.