Editing Arsenopyrite (section)

==Crystallography==
[[File:Arsenopyrite-176706.jpg|thumb|left|upright|Arsenopyrite crystal from the Yaogangxian Mine, Hunan, China (size: 2.7 x 2.0 x 1.7 cm)]]
Arsenopyrite crystallizes in the [[monoclinic]] [[crystal system]] and often shows prismatic crystal or columnar forms with [[Striation (geology)|striation]]s and [[Crystal twinning|twinning]] common. Arsenopyrite may be referred to in older references as [[orthorhombic]], but it has been shown to be monoclinic.  In terms of its atomic structure, each Fe center is linked to three As atoms and three S atoms.  The material can be described as Fe<sup>3+</sup> with the diatomic trianion AsS<sup>3−</sup>.  The connectivity of the atoms is more similar to that in [[marcasite]] than [[pyrite]].  The ion description is imperfect because the material is semiconducting and the Fe-As and Fe-S bonds are highly [[covalent]].<ref>Vaugn, D. J.; Craig, J. R. Mineral Chemistry of Metal Sulfides" Cambridge University Press, Cambridge: 1978. {{ISBN|0-521-21489-0}}.</ref>

[[File:Arsenopyrite by petrographic microscope NL.jpg|thumb|upright|Microscopic picture of arsenopyrite]]