Which one of the following is anisotropic in nature?

Anisotropy refers to materials whose physical properties, such as refractive index, electrical conductivity, and mechanical strength, vary depending on the direction of measurement. Crystalline solids, except those with cubic symmetry, are typically anisotropic. Quartz is a prominent example of an anisotropic crystalline material, exhibiting direction-dependent properties like birefringence, optical activity, and hardness. In contrast, isotropic materials show identical properties in all directions. Glass is a classic example of an isotropic material because of its amorphous, disordered internal structure. Similarly, rubber and most common plastics (amorphous polymers) are generally considered isotropic from a macroscopic perspective because their macromolecular chains are chaotically distributed, compensating for any local polarizability [1]. Therefore, among the given options, quartz is the only material that is inherently anisotropic due to its ordered crystalline structure.

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC10096153/