Morphology dominated rapid oxidation of framboidal pyrite

Abstract

The rapid oxidation of framboidal pyrite is conventionally attributed to its fine grain size. However, the effect of the crystal facets of the microcrystals in the framboids on the oxidation process has been overlooked. We synthesised pyrite monocrystals of microscopic size with both {100} and {111} facets, which are two major forms of framboidal pyrite crystals, in order to examine the oxidation behaviour of pyrite framboids. The results showed that the oxidation rate of microcrystals with a greater proportion of {111} facets was approximately 2 times higher than that of those with a greater proportion of {100} facets although the latter's size was smaller. Such a difference makes framboidal pyrite with {111} facets more sensitive to oxidative weathering in geochemical cycles than other forms of pyrite. These findings emphasise the role of crystal anisotropy in controlling the oxidation of framboidal pyrite, thereby suggesting that the shape controlled oxidation of pyrite is a potential indicator of the local redox conditions of the palaeoenvironment where it occurred.

Investigating the oxidation mechanism of facet-dependent pyrite: implications for the environment and sulfur evolution

“…Previously studies have indicated that SSA is one of the factors in the oxidative dissolution of minerals. 26,27 Although FeS 2 (100) exhibits a higher SSA than FeS 2 (210) in this work, it shows a lower oxidation rate compared with FeS 2 (210). Therefore, the difference in the oxidation rates between the two pyrite samples may be attributed to their distinct surface chemical or electrical properties, which will be discussed further below.…”

Facet-Dependent Productions of Reactive Oxygen Species from Pyrite Oxidation

“…The highly crystalline structure of as-synthesized pyrite was further confirmed by the presence of distinctive peaks in the XRD spectra (Figure 2b). XRD peaks were located at 28.5°, 33.1°, 37.1°, 40.8°, 47.4°, and 56.3°, corresponding to the {111}, {200}, {210}, {211}, {220}, and {311} crystal facets, respectively, 23 consistent with pure pyrite crystals [Joint Committee on Powder Diffraction Standards (JCPDS) number 42-1340]. The surface areas of as-prepared pyrite were 4.6, 3.9, 3.9, 3.7, 3.3, and 3.2 m 2 g −1 , respectively, according to the BET analysis (Table S2 of the Supporting Information).…”

Effects of chemical weathering on the exceptional preservation of mineralized insects from the Crato Formation, Cretaceous of Brazil: implications for late diagenesis of fine-grained Lagerstätten deposits

“…Oxidized pyrites often have an oxidation shell and an unoxidized core. Du et al (2021) noted that the degree of pyrite oxidation is relative to the thickness of the oxidation shell. Therefore, the thickness of the oxidation shell indicates a more oxidizing environment or a longer duration of oxidation.…”