Editing Bornite (section)

==Mineralogy==
Bornite is an important copper ore mineral and occurs widely in [[porphyry copper deposit]]s along with the more common [[chalcopyrite]]. Chalcopyrite and bornite are both typically replaced by [[chalcocite]] and [[covellite]] in the [[Supergene (geology)|supergene]] enrichment zone of copper deposits. Bornite is also found as disseminations in [[mafic]] [[igneous rock]]s, in [[Metamorphism|contact metamorphic]] [[skarn]] deposits, in [[pegmatite]]s and in [[Sedimentary rock|sedimentary]] cupriferous [[shale]]s.<ref name=Handbook/> It is important as an [[ore]] for its [[copper]] content of about 63 percent by mass.<ref name=Webmin/>

===Structure===
[[File:Bornite by petrographic microscope.jpg|thumb|Microscopic picture of Bornite]]
At temperatures above {{convert|228|C}}, the structure is [[Cubic crystal system|isometric]] with a unit cell that is about 5.50&nbsp;Å on an edge. This structure is based on cubic close-packed [[sulfur]] atoms, with copper and iron atoms randomly distributed into six of the eight [[Tetrahedron|tetrahedral]] sites located in the octants of the cube. With cooling, the Fe and Cu become ordered, so that 5.5&nbsp;Å subcells in which all eight tetrahedral sites are filled alternate with subcells in which only four of the tetrahedral sites are filled; symmetry is reduced to [[Orthorhombic crystal system|orthorhombic]].<ref name=Nesse>Nesse, William D., "Sulfides and Related Minerals" in ''Introduction to Mineralogy,'' New York: Oxford University Press, 2000, p 429</ref>

===Composition===
Substantial variation in the relative amounts of copper and iron is possible and [[solid solution]] extends towards chalcopyrite (CuFeS<sub>2</sub>) and [[digenite]] (Cu<sub>9</sub>S<sub>5</sub>). Exsolution of blebs and [[lamella (materials)|lamellae]] of chalcopyrite, digenite, and chalcocite is common.<ref name=Nesse/>

===Form and twinning===
Rare crystals are approximately cubic, [[Dodecahedron|dodecahedral]], or [[Octahedron|octahedral]]. Usually massive. Penetration twinning on the [[Miller index|crystallographic direction]], {111}.<ref name=Nesse/>