Which term describes possessing different physical or optical properties in different crystal directions?

• A. Crystal Axes
• B. Doubly Refractive (anisotropic)
• C. Crystal Planes
• D. Crystal Shape (form)

Answer: (B)

The main idea is directional dependence of properties in crystals, known as anisotropy. In many crystals, properties like the refractive index vary with direction because of the ordered lattice. When light passes through an anisotropic crystal, it can split into two rays traveling at different speeds and with different polarizations—this is double refraction, or birefringence. So the term that best fits “possessing different physical or optical properties in different crystal directions” is doubly refractive (anisotropic). The other terms don’t describe this directional variation: crystal axes are just reference directions inside the crystal, crystal planes are orientations of the lattice planes, and crystal shape (form) is the external geometry.