Pyrite dissolution at ambient temperatures is one of the important reactions in biogeochemical processes. It is related to the formation of acid mine drainage, where iron- and sulfur- oxidizing bacteria often grow actively and play an important role in pyrite weathering. In this article experimental studies on the oxidation of pyrite are reviewed, including pretreatment method to obtain the well-defined surface of pyrite particles, the mechanisms of pyrite oxidation by both bacteria and oxidizing agents (Fe(III) ions and oxygen), and suppressing factors of the reactions. Microbially mediated dissolution of pyrite in acidic environments proceeds mainly by the indirect contact mechanism of the iron-oxidizing bacteria, Thiobacillus ferrooxidans, that is, the bacteria mainly take part in the oxidation of Fe(II) ions to Fe(III) ions. Therefore, to suppress the weathering the reaction of pyrite with Fe(III) ions must be inhibited. In addition to the reduction and complexation of Fe(III) ions, masking of active sites on the pyrite surface by the preferential adsorption of other species is the most important factor. Based on the experimental studies, utilization of natural organic acids involved in botanical wastes is proposed for remediation and prevention of damage caused by acid mine drainage due to pyrite weathering.

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A lot of troilite reaction rim textures formed through sulfidation of FeNi alloy of kamacite and taenite with sulfur rich gas have been identified especially in CO3 unequilibrated carbonaceous chondrites. Troilite formation through sulfidation of FeNi alloy of kamacite and taenite with sulfur rich gas in the solar nebula is expected from the reaction kinetics as well as from the equilibrium condensation theory. On the other hand, heating experiments of mixtures including metallic iron grains and troilite powder show that troilite rim textures can be formed on chondrite parent body. Recent study shows that troilite reactionrim textures are more abundant for higher petrologic subtype (≥ 3.2). This would mean that sulfidation of metallic iron would have also proceeded in CO3 parentbody when petrologic subtype in CO3s is due to thermal metamorphism in CO3 parent body.

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High-resolution transmission electron microscopy (HRTEM) has been successfully applied to the observation of layer sequences and microstructures of clay minerals. However, there are some technical problems for the observation because of the characteristics of clay minerals such as crystallinity, expandability, and so on. This paper describes some practical problems and techniques including sample preparation and observation methods when we observe clay minerals by HRTEM.

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