Anisotropy of crystal means that the periodicity and density of atomic arrangement are different in different directions of crystal lattice, which leads to different physical and chemical characteristics of crystal in different directions, which is crystal anisotropy. Anisotropy of crystals is reflected in that the elastic modulus, hardness, fracture resistance, yield strength, thermal expansion coefficient, thermal conductivity, resistivity, electric displacement vector, polarization strength, magnetic susceptibility and refractive index of crystals are different in different directions.

Isotropy: the property that physical properties do not change with the direction of measurement. That is, the performance measured in different directions of the object shows the same value. If all gases, liquids (except liquid crystals) and amorphous objects are isotropic, then polycrystals are isotropic. For example, although metals and rocks have no regular geometry and have the same physical properties in all directions, they are essentially crystals and have a certain melting point because they are composed of many particles. Because the arrangement of grains in spatial orientation is irregular, the whole metal is isotropic.

The mechanical strength, elasticity and hardness of crystal and amorphous are compared by experiments.