Mechanisms and causes of changes in the shape of crystals during their growth

The relevance of this paper consists in the further development of a new direction in mineralogical crystallography — dynamic crystallomorphology, which allows one to obtain information on physical and chemical conditions of formation of mineral deposits by changing the form of crystals during their growth. Purpose of the work: theoretical substantiation and development of the method of morphokinetic analysis and methods for constructing morphogenetic diagrams of natural crystals. Research methodology: the study of mechanisms and causes of the change in the shape of crystals based on the observed mineralogical facts and idealized geometric models, as well as morphometric analysis of combination shapes of crystals. Results. Four kinematic mechanisms for preserving and changing the shape of crystals are considered. It is proved that the crystal shape of a certain min eral is directly determined by the supersaturation of the solution (undercooling a melt, the pressure of supersaturated vapor). All other factors, such as temperature, pressure, pH, redox potential Eh, activity of other ions involved in the mineral-forming process, affect the shape of crystals indirectly changing the solution supersaturation. It was shown that, depending on the direction and rate of change of supersaturation, 7 morphogenetic rows of closed or quasi-closed simple crystallographic forms (SCF) can be distinguished in each class of symmetry. Each row represents a SCF sequence in which each successive SCF replaces the previous one. Morphogenetic series were distinguished: 1) regressive evolutionary; 2) progressive evolutionary; 3) regressive intermittent; 4) progressive intermissive; 5) regressive shocking; 6) progressive shocking; 7) variable. A method is proposed for constructing morphogenetic diagrams using a diagram for a regressive evolutionary SCF series as an example (m3m symmetry of a cubic syngony). The morphogenetic diagram is given of the variable series based on the example of a particular cassiterite crystal