the condition or quality of changing in color or luster depending on the angle of light, especially of a gemstone that reflects a single shaft of light when cut in cabochon form. — chatoyant, adj.

What color is Chatoyancy?

It has greenish yellow color that makes it even more similar to feline eyes. Chatoyancy is traditionally attributed to tiny needles of exsolution rutile, although other mineral species can be also involved. These inclusions are so thin that they are not distinguishable to the naked eye and even through 10x loupe.

How is Chatoyancy formed?

Chatoyancy occurs when a band of light is reflected from a series of thin inclusions which are parallel to each other (these may be hollow tubes or needle-like crystals of, for example, rutile or haematite). In order to display this effect there must be enough fibres oriented in parallel to the base of the stone.