Gems : Cats Eyes

True cat's eye is a variety of chrysoberyl, either green to yellow-green or brown to yellow-brown, and is related to alexandrite. It is a rare and valuable gemstone, which is often underrated as being a "semi-precious" stone.
Chatoyancy is from the French chatoyer, which literally means ‘to shimmer like a cat's eye’. The effect is best seen in this variety of chrysoberyl, but is also found in a few other gemstones, such as sapphire or tourmaline. Tube-like or needle-like crystals running along the length of the stone give a strongly banded effect. Cat's eye chrysoberyls are always cut en cabochon – into beads – to show off their spectacular effect to it best.