What is birefringence and does diamond show it?

• A. Birefringence is double refraction; diamond is essentially isotropic and shows no observable birefringence.
• B. Birefringence refers to color dispersion.
• C. Birefringence is a measure of hardness.
• D. Only synthetic stones exhibit birefringence.

Answer: (A)

Birefringence is double refraction: in certain crystals that have directional dependence in their optical properties, light splits into two rays that travel at different speeds and become polarized differently. Diamond, with its cubic crystal system, is optically isotropic, meaning its refractive index is the same in all directions. Because of this symmetry, light does not split into two rays as it passes through a diamond, so there is no observable birefringence in a typical gem. In practice, you might hear of tiny birefringence only if there are internal strains or defects, but for a well-cut natural diamond, the effect is effectively negligible.

Color dispersion is a different phenomenon (how a material separates colors), hardness is about scratch resistance, and birefringence can occur in many natural crystals, not just synthetics.