Crystalline solids

Crystalline solids possess three characteristic properties that set them apart. First, there is regularity and periodicity in the arrangement of their constituent particles, with this ordered arrangement extending over a long range throughout the solid. Second, crystalline solids have sharp melting points -- they melt at one definite, characteristic temperature rather than over a range. Third, with the exception of substances having a cubic structure, crystalline solids are anisotropic: properties such as refractive index and thermal or electrical conductivity have different values when measured along different directions of the same crystal, because the arrangement of particles itself differs from direction to direction.