Word Wednesday: Chatoyancy

Welcome to Word Wednesday, Wolfstone Rock Shop’s weekly look at the language of rocks, minerals, and gems.

Chatoyancy (sha-TOY-an-see) is the cat’s-eye effect: a bright band of reflected light that appears to glide across a gemstone as the stone or light source moves.

What creates the moving line?

The effect occurs when light reflects from many closely aligned fibers, channels, tubes, or needle-like inclusions inside the material. A skilled cutter usually shapes the stone as a rounded cabochon and aligns those internal features so the band appears sharp and centered.

Familiar examples

Tiger’s-eye is a common chatoyant material. Chrysoberyl can produce an especially crisp cat’s-eye and, in the gem trade, the unqualified name “cat’s-eye” traditionally refers to chrysoberyl. Quartz, tourmaline, apatite, and other materials can also show chatoyancy.

Collector tip

View a suspected chatoyant stone under a single strong light and rotate it slowly. A real optical effect should respond naturally to changing light and viewing angle; the effect itself does not identify the mineral.

See this texture and other mineral features in person at Wolfstone Rock Shop, 1857 N Casaloma Dr, Appleton, WI 54913. Inventory changes often, so call (920) 809-8577 if you are looking for a particular example.