Isotropic An isotropic medium (water, air etc.) has the same properties in all directions: (speed of sound, speed of light, transparency, hardness etc.).

Anisotropic Anisotropic media have properties that are dependent on direction. For example, Calcite, (a pure crystalline form of CaCO3, also known as Iceland Spar), is double refracting. Two images of the print appear in the illustration below.