Introduction

Fundamental crystallogenesis can be divided into three stages of development differing in the extent of theoretical generalization. Qualitative theories providing a basis for the first stage, comprising processes of crystallization in single-component gaseous or melt systems, have been already developed. The second stage, which encompasses processes of crystal formation in binary systems and also those in aqueous solutions, is based on satisfactory developed qualitative notions also including some quantitative concepts. The third stage should be distinguished as encompassing processes occurring in multicomponent and polymineral media, where crystallization is complicated by a metasomatic constituent, i.e., chemical reactions of salting-in and salting-out, which manifest themselves in a correlated combination of growth and dissolution processes. According to their main distinctive features, here such processes are referred to as “polymineral-metasomatic crystallogenesis.”

Interaction of crystals and aggregates with solutions must be primarily regarded as a physicochemical process. Crystal growth, which is unaffected by dissolution of another substance and caused by a change in temperature, pressure, and solution concentration, is referred to as “ordinary” or “direct” growth. “Ordinary” or “direct” dissolution should be defined analogously. Metasomatic substitution means a process consisting in spatiotemporally correlated stages of dissolution of a protocrystal and precipitation of a new formation having a composition differing from that of the protocrystal.