The cat’s-eye effect is commonly observed in chrysoberyl and which of the following stones?

• A. Tourmaline
• B. Garnet
• C. Opal
• D. Emerald

Answer: (A)

Cat's-eye effect, or chatoyancy, occurs when light reflects from many tiny, aligned inclusions or fibrous structures inside a gem, producing a bright, single band that moves across the surface as the stone is rotated. Chrysoberyl is the classic example because its numerous fine rutile needles run parallel, creating a sharp, well-defined eye. Tourmaline can also display this phenomenon when its internal fibers or needle-like inclusions align to form a single reflective line, giving a cat's-eye look. Opal mainly shows play-of-color rather than a defined cat's-eye band, emerald typically does not exhibit true cat's-eye, and garnet can show it only in rare cases. So tourmaline is the best match with chrysoberyl for the cat's-eye effect.