CRYSTAL GENESIS OF CALCITE FROM SULFUR DEPOSITS OF PRYKARPATTYA

Abstract

The crystal genesis of calcite from sulfur deposits of Prykarpattya is examined with consideration of the influence of crystal structure and mineral formation conditions on the morphology of polyhedra. Published data on methods for predicting the morphological importance of crystal faces are systematized, including the Donnay–Harker corrected reticular density approach (BFDH), the Hartman-Perdok periodic bond chain (PBC) vector method, surface energy estimation, and Shafranovsky’s face symmetry criterion. The applicability of these methods to calcite is analyzed. It is shown that geometrical methods based solely on reticular density do not always adequately reproduce the real morphology, whereas approaches that account for periodic bond chains and surface energies are more physically substantiated. Samples from sulfur deposits display a wide spectrum of simple forms: the pinacoid {00.1}, the prism {10.0}, a series of rhombohedra, scalenohedra, and hexagonal dipyramids, among which {02.1}, {40.1}, and {21.1} are habit-defining. The observed morphological diversity is explained by the combined effect of structural factors (the mixed ionic–covalent character of the Ca²⁺–CO₃²⁻ bond, spatial features of the R3С space group, and PBC vectors) and the physicochemical conditions of crystallization. The influence of impurities, particularly Li⁺, on the stabilization of specific faces and modification of crystal habit is considered. Directions for further research are outlined, including the study of rare forms and the quantitative evaluation of face ratios in different genetic types of deposits.