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 stone's surface. As the direction of light changes, the band of light moves.
In stones like tigers eye, chatoyance gives 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 shaped as a cabochon.
The minerals best known for being chatoyant are tigers eye and chrysoberyl (cats eye), but it can also be seen in several other minerals.
The word 'chatoyant' originates from the French for 'cat's eye'.
Sadly, capturing chatoyance in a photo is extremely difficult because it's totally dependent on the angle of light and the angle from which the stone is viewed.
It's most visible when the stone or light source moves. A photograph, being a static image, lacks the ability to show how this band of light shifts and flows.
Article Picture
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 image.
