THE THERMAL MACROSTRUCTURE CHANGES IN THE NATURAL PHLOGOPITE CRYSTALS. V.M.Kalikhman, G.A.Kuznetsova, M.S.Metsik. Irkutsk State University, Irkutsk, Russia.

The thermal changes in real macrostructure of phlogopite in the temperature range from 300 to 1300 K have been investigated by the high-temperature X-ray diffractometry method. The monocrystals content the microadmixture of vermiculite and chlorite phase.

The microstructural changes have been determined as the half-width of basal difractional reflections B₀₀₁₂. B₀₀₁₂ of only few natural and synthetic fluorphlogopite crystals have been determined to be the same in the thermal range before the formation of high-temperature phase. Another group of specimens was characterized by increase B₀₀₁₂ in the temperature range 350-470 K. Lastly B₀₀₁₂ was changes for big group of the investigated crystals at the temperature over 600 K.The half-width of difractional reflections B₀₀₁₂ has been determined to be constant for the nonadmixtural phlogopite crystals .The low-temperature increase B₀₀₁₂ has been observed for the phlogopite crystals with vermiculite admixture. It corresponded to the decrease of phlogopite layer thickness because of vermiculite phase dehydrotation and followinges water migration out of the crystal .The chang of B₀₀₁₂ were observed in phlogopite monocrystals contenting the chlorite microadmixture at the temperature over 600 K. Thus individual thermal characterictics of monocrystal phlogopite macrostructure have been determined to be depend strongly on admixtural crystal phase.