What is Chatoyance in Rocks and Minerals?

Chatoyant, Chatoyance, and Chatoyancy

Chatoyance is an optical phenomenon that can be seen in certain rocks, minerals, and gemstones. The words chatoyant, chatoyance, and chatoyancy are all used to describe the same optical effect.

Chatoyance is caused when light reflects off fibrous inclusions or parallel internal structures within a stone.  

It produces a narrow band of reflected light from beneath the stone's surface. As the direction of light changes, this band 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'.

Chatoyance is best seen in stones cut as cabochons, as the curved surface allows light to interact with aligned internal fibres, producing a single, moving band of light rather than dispersed reflections.

The strength of the effect also depends on the cutter’s skill, because the fibrous structures responsible for chatoyance must be aligned parallel to the surface of the stone.

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 either the stone or the light source moves.

Article Picture

The stones in our picture are elbaite, which is a variety of tourmaline. Photo: Courtesy of Stan Celestian.