Surfaces, interfaces and crystal growth of marcasite FeS₂

Marcasite mineral is a metastable iron sulphide, α-FeS₂ , less known and less abundant than pyrite β-FeS₂ . Their chemical compositions are similar, formed by S₂^2- dimers and Fe²⁺ species, but the marcasite crystal structure is orthorhombic while pyrite is cubic. The thermodynamic stability of a range of selected surfaces and their kinetic growth are analysed with molecular mechanics simulations implemented in METADISE code. The most stable surface of marcasite corresponds to the (101) surface having the lowest surface energy (marcasite γ₁₀₁ = 1.06 Jm^-2) and the most favoured kinetic growth rate is expected for the [010] direction (the attachment energy of (010) surface is 0.20 |eV|/at). Mirror twinning is another characteristic of the mineral contributing to a distinctive crystal growth forming different shapes such as striated needles or pseudo-pentagonal flowers. Similarities, differences and overgrowth between the two dimorphs are highlighted. (author)