Which stones are known for strong pleochroism?

• A. Emerald
• B. Emerald and Ruby
• C. Emerald, Ruby, Sapphire
• D. Emerald, Ruby, Sapphire, and Tanzanite

Answer: (D)

Pleochroism happens when a crystal absorbs light differently along its various crystallographic directions, so a gemstone can show different colors as you rotate it. Emerald, ruby, and sapphire are classic examples because their crystal structures cause noticeable color shifts along different axes. Emerald typically appears yellow-green in one direction and green in another, while sapphire and ruby show distinct color changes (blue vs yellow/orange for sapphire, red to pinkish or purplish for ruby). Tanzanite is also strongly pleochroic, revealing blue, violet, and burgundy hues depending on orientation. Since all four gems exhibit pronounced color changes with viewing direction, the best answer includes all of them.