Which gem often shows pleochroism visible without a magnifying device?

• A. Ruby
• B. Emerald
• C. Opal
• D. Tanzanite

Answer: (D)

Pleochroism is when a gemstone appears to show different colors as you view it from different directions because the crystal absorbs light differently along its axes. Some stones reveal this color change clearly enough to notice without any magnification, while others need a loupe or microscope to see the shift.

Tanzanite is famous for strong, eye-visible pleochroism. It typically shows blue and violet depending on the viewing direction, so rotate the stone and you’ll often see a distinct color change with the naked eye. This pronounced two-color behavior makes the effect easy to detect without magnification.

Ruby and emerald do exhibit pleochroism, but the color shifts are usually subtler and less obvious to the unaided eye. Opal’s characteristic play-of-color comes from diffraction within its microstructure, not from pleochroism, so its color changes aren’t described in terms of absorption along crystal axes.