A good analogy for the chatoyance effect is how light reflects to form a line across the surface of a spool of silk thread. Viewing and moving a spool of silk thread under a beam of incident light can be a useful way to develop an understanding of how parallel inclusions produce an “eye” within a gemstone.

In a chatoyant gemstone, the band of light will move back and forth beneath the surface of the gem as it is turned under a beam of incident light. The band will also move if the position of the light is moved, or the observer moves his head to view the stone from a different angle. The motion of the cat’s-eye across the top of the gem is one of the things that makes these stones so interesting, beautiful, and desired by many people.