Can You Name These Gemstone Optical Effects? A 60-Second Challenge

Gemstones do more than sparkle. Some perform optical tricks so dramatic that one tilt can change the entire stone.

The challenge

Blue flash sliding over a gray stone: Labradorite — labradorescence.

A moving band of light on a cabochon: Cat’s-eye chrysoberyl — chatoyancy.

A star appearing under one light: Star ruby or sapphire — asterism.

Different colors from different directions: Tanzanite or iolite — pleochroism.

Green in daylight, reddish under warm light: Alexandrite — color change.

Rainbow colors in a pale cabochon: Opal — play-of-color.

Gemology rule: An optical effect can support identification, but it is not a complete identification by itself. Lighting, cut, and treatment can all change what you see.

How many did you know before reading the answers? Send this to the friend who always says every shiny stone is a diamond.