Editing Pyrite (section)

==Formal oxidation states for pyrite, marcasite, molybdenite and arsenopyrite==

From the perspective of classical [[inorganic chemistry]], which assigns formal oxidation states to each atom, pyrite and marcasite are probably best described as Fe<sup>2+</sup>[S<sub>2</sub>]<sup>2−</sup>. This formalism recognizes that the sulfur atoms in pyrite occur in pairs with clear S–S bonds. These [[Disulfide|persulfide]] [<sup>−</sup>S–S<sup>−</sup>] units can be viewed as derived from [[hydrogen disulfide]], H<sub>2</sub>S<sub>2</sub>. Thus pyrite would be more descriptively called iron persulfide, not iron disulfide. In contrast, [[molybdenite]], [[molybdenum|Mo]]S<sub>2</sub>, features isolated sulfide S<sup>2−</sup> centers and the oxidation state of molybdenum is Mo<sup>4+</sup>. The mineral [[arsenopyrite]] has the formula Fe[[arsenic|As]]S. Whereas pyrite has [S<sub>2</sub>]<sup>2−</sup> units, arsenopyrite has [AsS]<sup>3−</sup> units, formally derived from [[deprotonation]] of arsenothiol (H<sub>2</sub>AsSH). Analysis of classical oxidation states would recommend the description of arsenopyrite as Fe<sup>3+</sup>[AsS]<sup>3−</sup>.<ref name=Vaughan>{{cite book |author1=Vaughan, D. J. |author2=Craig, J. R. |title=Mineral Chemistry of Metal Sulfides |publisher=Cambridge University Press |location=Cambridge, UK |year=1978 |isbn=978-0-521-21489-6}}</ref>