asteriated

Asteriated is an adjective used to describe something that exhibits asterism, which is a phenomenon where certain crystals appear to display a star-like shape when viewed from certain directions. This star effect is typically seen in gemstones, most notably in star sapphires and star rubies, which are varieties of corundum. Other minerals that can exhibit asterism include garnet, chrysoberyl, and tourmaline.

The asterism is caused by the presence of needle-like inclusions of a mineral, such as rutile (titanium dioxide), within the gemstone. These inclusions are aligned in specific crystallographic directions. When light enters the crystal and reflects off these inclusions, it creates a bright, sharp, star-shaped pattern, usually with four, six, or even twelve rays. The visibility and sharpness of the star depend on the quality of the inclusions, their alignment, and the cut of the gemstone. A cabochon cut, which is a smooth, rounded, and domed cut, is most commonly used for asteriated gemstones as it best displays the star effect. The star is typically seen centered on the dome of the cabochon.