Abstract 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 S22- 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 γ 101 = 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.

Surfaces properties of TiO2 in the brookite phase and the lithium diffusion are studied using density functional theory (DFT) and interatomic potential simulations. Simulations predict that the brookite surfaces have a higher intrinsic Lewis acidity compared to the other polymorphs due to the presence of four coordinated Ti atoms on the surface in contrast to the most stable surfaces of anatase and rutile which have five coordinated Ti surface atoms. The surface reactivity of the brookite is then expected to be higher for catalysis. The (210) surface is the most stable calculated surface and some experimental morphologies have been revisited. Regarding Li intercalation, the migration occurs along the c-direction and open channel surfaces are desired, therefore particles exposing the (001) surface. Those differences on chemical/physical properties highlight the importance to control the nanoparticle shapes for a given application.

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/m2 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.