Pleochroism is a change in color or intensity seen when you rotate a transparent crystal and view it from different directions. It happens because light is absorbed differently along different crystal directions. Collectors most often notice pleochroism in minerals like tourmaline and iolite, especially in clearer pieces. The effect is easiest to see under steady light when you rotate the crystal rather than moving the light source.
To check Pleochroism, hold the crystal in front of a strong, fixed light and rotate it slowly while looking through the thickest clear section. Write down the two most distinct colors or intensity states you see because that is the collector-relevant result. Don’t confuse pleochroism with surface staining—staining does not change when you rotate the viewing direction through the crystal. If the specimen is zoned, note zoning separately; pleochroism changes with direction, while zoning stays fixed in place.
Pleochroism vs. color zoning Zoning is fixed within the crystal. Pleochroism changes as you rotate and view through different directions.
Pleochroism vs. surface staining Stain sits on the surface. Pleochroism is seen through the interior and shifts with direction.
Pleochroism vs. lighting changes Moving the light can mimic a shift. Keep the light fixed and rotate the crystal instead.
Pleochroism vs. thickness effects Thick areas look darker regardless of direction. Compare similar thickness while rotating.