Asterism (star-effect)

Asterism, or star, is a rare lighteffect in natural precious stones.

Starlike rays of light observed in some minerals when viewed from certain directions, particularly if the mineral is cut en cabochon. Minerals having this feature are called asteriated or star. Asteriated beryl, chrysoberyl, crocidolite, emerald, quartz, ruby, and sapphire are known.