Final answer:
Isotropic minerals have uniform properties in all directions, while anisotropic minerals exhibit properties that depend on the measurement direction due to their varied internal molecular arrangement, causing phenomena like birefringence.
Step-by-step explanation:
The distinction between isotropic and anisotropic minerals refers to their internal structure and how this structure affects their physical properties. Isotropic minerals have uniform properties in all directions. This means that their molecular arrangement does not change the way the mineral behaves physically when measured from different directions. In contrast, anisotropic minerals have a varied arrangement of molecules, which causes their properties to depend on the direction in which they are measured.
Anisotropic minerals display different behaviors such as light refraction, hardness, electrical conductivity, and heat conductivity based on the direction of measurement. Birefringence is a common phenomenon in anisotropic minerals, like calcite, which can split a beam of light into two beams with different indices of refraction. This is because of the different orientations and arrangements of atoms within the crystal lattice. Isotropic minerals, such as garnet, do not exhibit this property because their molecular structure is the same in all directions.