The temperature range of melting of crystalline material

The first-order phase transition is accompanied by an increase in disordering. Defects and dislocations of the crystal cell decrease the temperature of the phase transition. Atoms located on the crystal surface get higher internal free energy first. Atoms located in different areas of the crystal have different numbers of saturated bonds. The lower the number of such bonds, the lower the temperature of the atom transition into the melt. The process of melting of two fractions (with sizes of 2 nm-0.1 mm and 1.5-2 mm) plagioclase, alkali feldspar, and quartz was studied at temperatures of 950, 1000, 1100, and 1200A degrees C. Surface melting of all mineral fragments occurred at a temperature of 950A degrees C.