Cat's eye

Cat's Eye describes a gemstone polished into a cabochon that displays a narrow band of concentrated light going accross the width of the stone. This effect, known as chatoyancy, or cat's eye effect, is caused by inclusions of fine, slender parallel mineral fibers in the gemstone that reflect light in a single band. Of all the gemstones that exhibit cat's eye, Chrysoberyl Cat's Eye is the best known. Chrysoberyl has the strongest and most distinct cat's eye effect of all gemstones. Though several different gemstones types exhibit a cat's eye effect, only Chrysoberyl's cat's eye enjoys the privilege of having the name "Cat's Eye" without any prefix. Whenever the term "Cat's Eye" is used, it refers to Chrysoberyl cat's eye by default, unless otherwise specified.

Other Cat's Eye gemstones include Cat's Eye Tourmaline, Cat's Eye Quartz, Cat's Eye Aquamarine, Cat's Eye Moonstone, Cat's Eye Apatite, and Cat's Eye Scapolite. Of all these other Cat's Eye Gemstones, Chrysoberyl has the greatest hardness.

Sources:

Cat's Eye sources are in Brazil, India, China, and Zimbabwe.