Blue Cat's Eye gemstone. It features a prominent oval cabochon with a distinct vertical light reflection, a phenomenon known as chatoyancy, which is characteristic of cat's eye stones. The pendant's design is typical of vintage or Y2K-era costume jewelry. Similar pieces are often found set in: Sterling Silver (.925): Frequently used for these types of pendants. Silver-tone Alternative possibilities for the blue stone include blue banded agate or blue chalcedony, although these typically show more visible internal banding or a more translucent, uniform color compared to the sharp chatoyancy of a cat's eye. The piece is also visually similar to some mood necklaces, which change color based on temperature.