Asterism is a phenomenon that occurs in certain gemstones, where a star-like pattern appears on the surface when viewed under a light source. This effect is typically seen in stones like star sapphire and star ruby, which contain needle-like inclusions that reflect light in a way that creates a star shape. The most common star pattern has six rays, but some stones can display four or twelve rays. The presence of asterism is due to the arrangement of these inclusions, often made of rutile or other minerals, within the gemstone. When cut in a cabochon shape, the stone's surface can enhance this optical effect, making it highly sought after in jewelry. Asterism adds unique beauty and value to gemstones, attracting collectors and enthusiasts alike.