Material: Minerals: Cat's Eye & Man-Made Cat's Eye tells us that, "Cat's Eye is a gemstone polished into a cabochon (polished gem without facets) that displays a narrow band of concentrated light going across 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.
"Chrysoberyl Cat's Eye is the best known of all cat's eye gemstones, and comes in blue, red, green, yellow, orange, brown, pink, purple, gray and multicolored." []

Man-Made Cat's Eye beads, or fiber-optic beads, are glass beads made by fusing quartz fibers together, in order to create the chatoyancy effect of a band of light through the center.