Understanding the Surfaces and Crystal Growth of Pyrite FeS2

Abstract

Pyrite is a common sulfide mineral, which has arisen early interest by its euhedral shape and by its metallic glow similar to gold. However, it is only in our century that we began to understand pyrite crystal growth, considering the thermodynamic and kinetic aspects of crystal formation as a function of temperature and concentration of the elements present in the medium. This article reports an analysis by molecular mechanics of 11 surfaces associated to observed morphologies in order to explain the growth of natural and synthesized minerals. The lowest surface and attachment energies (respectively 1.04 J/m 2 and-20.3 kJ/mol) were obtained for the (001) plane, indicating that it is the most stable surface and that kinetic growth also preferentially occurs on this plane. Less known properties, such as crystal striations along the <100> directions, are also discussed.

Processes of metastable-mineral formation in oxidation zones and mine waste

“…For simple systems other than oxides, the experimental or computational results on their surface energies are limited. Surface energy of pyrite (Raichur et al , 2001; Arrouvel and Eon, 2018) is comparable to those of the iron oxides. However, a systematic view of the equilibria between the iron sulfides, including the surface-area effects, is missing.…”

Surfaces, Interfaces and Crystal Growth of Marcasite FeS2

“…The methodology to simulate marcasite is the same than the one described in the previous study by Arrouvel and Eon 19 , using identical interatomic potentials that have been previously validated on pyrite by de Leeuw et al 20 . The method implemented in the computer simulation code METADISE 21 [2] where r 0 is the separation between the two sulphurs (dimer S1-S2) at equilibrium.…”

“…The force field simulations have been applied successfully to pyrite 19,20 and prove to be transferable to marcasite having the same chemical nature. The optimized structural parameters, elastic and dielectric properties of the dimorphs are listed in Table 2.…”

“…The mineral is then easiest to distort upon a shear stress rather than compression. Some properties extracted from force field methods on pyrite have been already discussed by Arrouvel and Eon 19 , are extended in Table 2 and compared to experimental data [31][32][33][34] . This dimorph is structurally isotropic, with 3 independent elastic constants.…”

“…The discrepancy corresponds to the family of planes perpendicular to S-S dimers which are orientated along the <111> directions. The {110} facet can also be stabilised through steps made of stable {001} facets (see Arrouvel and Eon 19 and references therein). However, the main exposed surfaces, thermodynamically stable and with higher growth rates, are in excellent agreement with ab initio and experimental studies.…”