Which term denotes possessing identical physical or optical properties in all crystal directions?

Which term denotes possessing identical physical or optical properties in all crystal directions?

• A. Grain lines
• B. Habit
• C. Macle
• D. Singly refractive (isotropic)

Answer: (D)

Identical physical or optical properties in all crystal directions describes isotropy. In crystals, an isotropic material has a single refractive index that doesn’t vary with direction, so light doesn’t experience birefringence and there’s no double refraction as you rotate the crystal. The term singly refractive (isotropic) captures this idea directly: it signals one refracted ray and uniform optical behavior in every direction. Cubic crystals often exhibit this symmetry, reinforcing the uniformity of their properties regardless of direction. The other terms relate to crystal form or features—grain lines mark boundaries between grains, habit is the typical shape a crystal grows into, and macle is a twinned, decorative pattern—so they don’t describe directional uniformity.

Identical physical or optical properties in all crystal directions describes isotropy. In crystals, an isotropic material has a single refractive index that doesn’t vary with direction, so light doesn’t experience birefringence and there’s no double refraction as you rotate the crystal. The term singly refractive (isotropic) captures this idea directly: it signals one refracted ray and uniform optical behavior in every direction. Cubic crystals often exhibit this symmetry, reinforcing the uniformity of their properties regardless of direction. The other terms relate to crystal form or features—grain lines mark boundaries between grains, habit is the typical shape a crystal grows into, and macle is a twinned, decorative pattern—so they don’t describe directional uniformity.