Don't be confused by the word Beryl in the name. Chrysoberyl is not a Beryl, but a separate type of gem altogether and is the third hardest naturally occurring gemstone which lies between corundum and topaz on the hardness scale.
In fact the name you probably know this gem by is Cats-Eye. This yellowy-green variety exhibits chatoyancy or opalescence that reminds us of an eye of a cat. When cut to produce a cabochon, the mineral forms a light-green specimen with a silky band of light extending across the surface of the stone. In particularly good specimens, it seems to open and close when the stone is turned. Fine cat's eyes should be of a distinctive colour and be as transparent as possible. The most popular ones are those of a beautiful honey yellow and those with fine green tones.