What is Chatoyance in Rocks and Minerals?
Chatoyant Chatoyance and Chatoyancy
Chatoyance is a reflectance that can be seen in certain rocks, minerals and gemstones.
The words chatoyant, chatoyance and chatoyancy are all used to describe this optical phenomenon.
Chatoyance is caused as light reflects off fibrous inclusions or cavities within a stone's structure.
It produces a narrow band of reflected light from beneath the surface of the stone. As the direction of light changes the band of light moves. In patterned stones this can give the impression of movement on the surface of the stone.
Where present, chatoyance becomes visible as light reflects off the stone from different angles. The effect can vary significantly and is best seen in gemstones that have been polished as a cabochon.
The minerals best known for being chatoyant are tigers eye and chrysoberyl (cats eye). It can also be seen in several other minerals.
The word originates from the French for "cat's eye".
The stones in our picture are elbaite which is a variety of tourmaline. Photo courtesy of Stan Celestian. The picture is clickable and redirects to the original photo.