The term cat's eye, or chatoyancy, is used to describe a phenomenal optical property in gemstones, in this case synthetic chrysoberyl. The effect, when present, appears as a bright, narrow slit similar to the pupils in the eyes of your favorite feline. This phenomenon is caused by parallel fibrous or needle-like inclusions that interfere with the passage of light throughout the crystal, scattering and reflecting light back to the viewer as a thin line. Chatoyant synthetic chrysoberyl is particularly incredible because it exhibits two rare phenomena in gemstones: both the cat's eye affect and color change. The term synthetic refers to a man-made material with a natural counterpart that shares the same (or nearly identical) chemical, optical, and physical properties. Synthetic color change chrysoberyl presents gem lovers with an opportunity to own the stunning color change effect so prized in gems.