Asterism (gemology)

Asterism is an optical phenomenon seen in some gemstones, characterized by a star-like pattern appearing on the surface when the stone is viewed under a light source. This effect occurs due to the presence of needle-like inclusions, usually made of minerals like rutile, which reflect light in specific ways. Common gemstones exhibiting asterism include star sapphires and star rubies. The quality of the star—in terms of clarity, size, and movement—can significantly enhance a gem's value and beauty, making it sought after among collectors and jewelry enthusiasts.