Cat's eye is a unique gemstone known for its striking optical phenomenon called chatoyancy, which resembles the slit-like pupil of a cat's eye. This effect occurs when light reflects off the stone's fibrous inclusions, creating a bright line that moves across the surface as the stone is turned. Typically found in chrysoberyl, tourmaline, and quartz, cat's eye gemstones come in various colors, including green, yellow, and brown. They are often used in jewelry, valued for their beauty and rarity. The gemstone is also believed to bring good luck and protection to its wearer.