, the quality of exhibiting properties with different values when measured along axes in different directions. Anisotropy is most easily observed in single crystal
s of solid element
s or compound
s, in which atom
s, or molecule
s are arranged in regular lattice
s. In contrast, the random distribution of particles in liquid
s, and especially in gas
es, causes them rarely, if ever, to be anisotropic.
A familiar example of anisotropy is the difference in the refractive index of light along different axes of crystals of the mineral calcite. Another example is the electrical resistivity of selenium, which is high in one direction but low in the other; when an alternating current is applied to this material, it is transmitted in only one direction (rectified), thus becoming a direct current.