Gemstone Color Change Phenomena


Step 2: Advanced Gemology

Lesson 3

gemstone color change - stillwellite
Although alexandrite and sapphire are well-known examples of gemstone color change, the phenomenon occurs in other materials, too. Stillwellite shows red under sunlight and halogen light but yellow under fluorescent light. “Stillwellite,” crystal on alkaline pegmatite matrix, Darai-Piez Massif, Alai Range, Tien-Shan Mountains, Tajikistan. © Rob Lavinsky, www.iRocks.com. Used with permission.

Frequently, people ask me to explain how gemstone color change works. Some stones can change color under different light sources. Although the answer is pretty complex, a few diagrams can really help.

To understand how this phenomenon works, you need to learn about light and how gems get their coloration.

White Light and Colors

We know that sunlight or white light contains all colors. Pass a sunbeam through a prism and you’ll see a rainbow on a nearby wall. You can also consider light as energy. Visible light is …

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