The decisive problems at present in the experimental investigation of rocks and minerals at high pressures and temperatures are the problems of studying processes which are going on inside using various physical methods. The most important avenue of experiments is investigation of changes of physical properties of the rocks and minerals at high pressures and temperatures. The majority of papers in this line give a quantitative assessment of the physical characteristics, establish factors these characteristics depend on, and major patterns of their variation at high pressure and temperature parameters. Aside of this, abnormal manifestations of physical properties of the rocks were revealed prior to destruction, in the dehydration processes and in the phase changes Levykin, 1991; Parkhomenko, 2000; Volarovich et al., 1974, 1975, 1979a. These investigations suggested that the abnormal changes of the rock physical parameters at high pressures and temperatures indicate to one or another process and are connected with the microstructure changes in the rocks and minerals. With allowance for the main direction, problems were set before the laboratory working on simulation and analysis of processes in the seismic zones to investigate a physical nature of the earthquake preparation processes and the attendant forerunners, at different scale levels, on the basis of experimental investigations of the rock and mineral properties and their variation at high pressures and temperatures. The neutron diffraction method, as the method possessing optimum capabilities among other microstructure methods of investigation of the matter, was selected as a physical investigation method. Calcite, that have received the most study at high pressure and temperature parameters and which is prevailing in the Earth, was selected as the first object of investigation.