Using the diffraction pattern video survey under varying conditions of tin heating and melting some specific features of deformation and crystal structure violations have been found out. In tin melting its crystal lattice points become nonequivalent in an energetic and configuration sense, as they have a different number of neighbours at different distances. The main reason of melting consists in the generation and extreme gain of microheterogeneity of the nearest atoms surroundings in the preliminary melting. This is not typical for a crystal and results in its unstable position. The specific features of the nearest order are generated even in a crystal and inherited by liquid from a preliminary melting structure.