Editing Goldschmidt classification (section)

==Chalcophile elements==
The chalcophile elements ({{ety|grc|''{{lang|grc|[[wikt:χαλκός#Ancient Greek|χαλκός]]}}'' ({{Transliteration|grc|khalkós}})|copper, brass, bronze', also 'ore}}) include [[Silver|Ag]], [[Arsenic|As]], [[Bismuth|Bi]], [[Cadmium|Cd]], [[Copper|Cu]], [[Gallium|Ga]], [[Germanium|Ge]], [[Mercury (element)|Hg]], [[Indium|In]], [[Lead|Pb]], [[Sulfur|S]], [[Antimony|Sb]], [[Selenium|Se]], [[Tin|Sn]], [[Tellurium|Te]], [[Thallium|Tl]] and [[Zinc|Zn]].<ref>Allaby, M. (2013). A dictionary of geology and earth sciences. Oxford University Press.</ref>

Chalcophile elements are those that remain on or close to the surface because they combine readily with [[sulfur]] and some other [[chalcogen]]s other than oxygen, forming compounds which did not sink along with iron towards the Earth's core. Chalcophile elements are those metals and heavier nonmetals that have a low affinity for oxygen and prefer to bond with sulfur as highly insoluble [[sulfides]].

Because these sulfides are much denser than the silicate minerals formed by lithophile elements, chalcophile elements separated below the lithophiles at the time of the first crystallization of the Earth's crust. This has led to their depletion in the Earth's crust relative to their solar abundances, though because the minerals they form are nonmetallic, this depletion has not reached the levels found with siderophile elements.

However, because they formed volatile hydrides in the [[Formation of the Solar System|accreting protosolar nebula]] when the controlling [[redox|redox reaction]] was the oxidation or reduction of hydrogen, the less metallic chalcophile elements are strongly depleted on Earth as a whole relative to cosmic abundances. This is most especially true of the chalcogens [[selenium]] and [[tellurium]] (which formed volatile [[hydrogen selenide]] and [[hydrogen telluride]], respectively), which for this reason are among the rarest elements found in the Earth's crust (to illustrate, tellurium is only about as abundant as [[platinum]]).

The most metallic chalcophile elements (of the copper, zinc and boron groups) may mix to some degree with iron in the Earth's core. They are not likely to be depleted on Earth as a whole relative to their solar abundances since they do not form volatile hydrides. [[Zinc]] and [[gallium]] are somewhat "lithophile" in nature because they often occur in silicate or related minerals and form quite strong bonds with oxygen. Gallium, notably, is sourced mainly from [[bauxite]], an [[aluminum hydroxide]] ore in which gallium ions substitute for chemically similar aluminum.

Although no chalcophile element is of high abundance in the Earth's crust, chalcophile elements constitute the bulk of commercially important metals. This is because, whereas lithophile elements require energy-intensive electrolysis for extraction, chalcophiles can be easily extracted by [[reduction (chemistry)|reduction]], and chalcophiles' geochemical concentration{{snd}}which in extreme cases can exceed 100,000 times their average crustal abundance. These greatest enrichments occur in high plateaus like the [[Tibetan Plateau]] and the Bolivian [[Altiplano]] where large quantities of chalcophile elements have been uplifted through [[plate tectonics]]. A side-effect of this in modern times is that the rarest chalcophiles (like [[Mercury (element)|mercury]]) are so completely exploited that their value as minerals has almost completely disappeared.