Which gem often has pleochroism strong enough to see without an instrument?

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

Answer: (D)

Pleochroism is when a gem shows different colors when viewed from different directions because the crystal absorbs light differently along its axes. This color change can be noticeable even without a loupe or microscope in stones with strong pleochroism. Tanzanite is famous for this effect, typically presenting blue and violet colors depending on how you turn the stone, and sometimes a brownish burgundy tint in other orientations. That striking naked-eye contrast makes its pleochroism easy to observe and a helpful clue in identification.

Sapphire can also show pleochroism, but the color differences are usually subtler and not always obvious without magnification. Emerald’s pleochroism exists as well, but the changes are often less dramatic and can be masked by inclusions. Opal does not exhibit pleochroism; its standout feature is play-of-color from diffraction rather than directional color change.