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TheGoldschmidt classification,[1][2]developed byVictor Goldschmidt (1888–1947), is ageochemical classification which groups thechemical elements within the Earth according to their preferred host phases into lithophile (rock-loving), siderophile (iron-loving), chalcophile (sulfide ore-loving orchalcogen-loving), and atmophile (gas-loving) or volatile (the element, or a compound in which it occurs, is liquid or gaseous at ambient surface conditions).
Some elements have affinities to more than one phase. The main affinity is given in the table below and a discussion of each group follows that table.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Group → | |||||||||||||||||||
| ↓ Period | |||||||||||||||||||
| 1 | 1 H | 2 He | |||||||||||||||||
| 2 | 3 Li | 4 Be | 5 B | 6 C | 7 N | 8 O | 9 F | 10 Ne | |||||||||||
| 3 | 11 Na | 12 Mg | 13 Al | 14 Si | 15 P | 16 S | 17 Cl | 18 Ar | |||||||||||
| 4 | 19 K | 20 Ca | 21 Sc | 22 Ti | 23 V | 24 Cr | 25 Mn | 26 Fe | 27 Co | 28 Ni | 29 Cu | 30 Zn | 31 Ga | 32 Ge | 33 As | 34 Se | 35 Br | 36 Kr | |
| 5 | 37 Rb | 38 Sr | 39 Y | 40 Zr | 41 Nb | 42 Mo | 43 Tc | 44 Ru | 45 Rh | 46 Pd | 47 Ag | 48 Cd | 49 In | 50 Sn | 51 Sb | 52 Te | 53 I | 54 Xe | |
| 6 | 55 Cs | 56 Ba |  | 71 Lu | 72 Hf | 73 Ta | 74 W | 75 Re | 76 Os | 77 Ir | 78 Pt | 79 Au | 80 Hg | 81 Tl | 82 Pb | 83 Bi | 84 Po | 85 At | 86 Rn |
| 7 | 87 Fr | 88 Ra |  | 103 Lr | 104 Rf | 105 Db | 106 Sg | 107 Bh | 108 Hs | 109 Mt | 110 Ds | 111 Rg | 112 Cn | 113 Nh | 114 Fl | 115 Mc | 116 Lv | 117 Ts | 118 Og |
| 57 La | 58 Ce | 59 Pr | 60 Nd | 61 Pm | 62 Sm | 63 Eu | 64 Gd | 65 Tb | 66 Dy | 67 Ho | 68 Er | 69 Tm | 70 Yb | |||||
| 89 Ac | 90 Th | 91 Pa | 92 U | 93 Np | 94 Pu | 95 Am | 96 Cm | 97 Bk | 98 Cf | 99 Es | 100 Fm | 101 Md | 102 No | |||||
Goldschmidt classification:LithophileSiderophileChalcophileAtmophileTrace/Synthetic
Lithophile elements (from Ancient Greek λῐ́θος (líthos) 'stone' and φίλος (phílos) 'dear, beloved') are those that remain on or close to the surface because they combine readily with oxygen, forming compounds that did not sink into theEarth's core. The lithophile elements includeAl,B,Ba,Be,Br,Ca,Cl,Cr,Cs,F,I,Hf,K,Li,Mg,Na,Nb,O,P,Rb,Sc,Si,Sr,Ta,Th,Ti,U,V,W,Y,Zr, and thelanthanides or rare earth elements (REE).
Lithophile elements mainly consist of the highly reactive metals of thes- andf-blocks. They also include a small number of reactive nonmetals, and the more reactive metals of thed-block such astitanium,zirconium andvanadium.
Most lithophile elements form very stableions with anelectron configuration of a noble gas (sometimes with additional f-electrons). The few that do not, such as silicon, phosphorus and boron, form strongcovalent bonds with oxygen, often involvingpi bonding. Their strong affinity for oxygen causes lithophile elements to associate very strongly withsilica, forming relatively low-density minerals that thus rose towards the crust duringplanetary differentiation. The more soluble minerals formed by thealkali metals tend to concentrate inseawater orarid regions where they can crystallise. The less soluble lithophile elements are concentrated on ancientcontinental shields where soluble minerals have been weathered.
Because of their strong affinity for oxygen, most lithophile elements are enriched in the Earth's crust relative to their abundance in theSolar System. The most reactive s- and f-block metals, which form either saline ormetallic hydrides, are known to be extraordinarily enriched on Earth as a whole relative to their solar abundances. This is because during the earliest stages of theEarth's formation, the abundance of stable forms of each element was determined by how readily it forms volatile hydrides; these volatiles then could "escape" the proto-Earth, leaving behind those elements unreactive with hydrogen. Under these conditions, the s- and f-block metals were strongly enriched during the formation of the Earth. The most enriched elements arerubidium,strontium andbarium, which between them account for over 50percent by mass of allelements heavier than iron in the Earth's crust.
The nonmetallic lithophiles – phosphorus and thehalogens – exist on Earth as ionicsalts with s-block metals inpegmatites and seawater. With the exception offluorine, whosehydride formshydrogen bonds and is therefore of relatively low volatility, these elements have had their concentrations on Earth significantly reduced through escape of volatile hydrides during the Earth's formation. Although they are present in the Earth's crust in concentrations quite close to their solar abundances, phosphorus and the heavier halogens are probably significantly depletedon Earth as a whole relative to their solar abundances.
Several transition metals, includingchromium,molybdenum,iron andmanganese, showboth lithophileand siderophile characteristics and can be found in both these two layers. Although these metals form strong bonds with oxygen and are never found in the Earth's crust in the free state, metallic forms of these elements are thought very likely to exist in the core of the earth as relics from when the atmosphere did not contain oxygen. Like the "pure" siderophiles, these elements (except iron) are considerably depleted in the crust relative to their solar abundances.
Owing to their strong affinity for oxygen, lithophile metals, although they form the great bulk of the metallic elements in Earth's crust, were never available as free metals before the development ofelectrolysis. With this development, many lithophile metals are of considerable value as structural metals (magnesium,aluminium,titanium,vanadium) or asreducing agents (sodium,magnesium,calcium).
The non-metals phosphorus and the halogens were also not known to early chemists, though production of these elements is less difficult than of metallic lithophiles since electrolysis is required only with fluorine. Elementalchlorine is particularly important as anoxidizing agent – usually being made by electrolysis ofsodium chloride.
Siderophile elements (from Ancient Greek σίδηρος (sídēros) 'iron') are thetransition metals which tend to sink towards the core duringplanetary differentiation, because they dissolve readily in iron either assolid solutions or in the molten state. Some sources[3] include elements which are not transition metals in their list of siderophiles, such asgermanium. Other sources may also differ in their list based on the temperature being discussed – niobium,vanadium,chromium, andmanganese may be considered siderophiles or not, depending on the assumed temperature and pressure.[4] Also confusing the issue is that some elements, such as the aforementionedmanganese, as well asmolybdenum, form strong bonds with oxygen, but in the free state (as they existed on the early Earthwhen free oxygen did not exist) can mix so easily with iron that they do not concentrate in the siliceous crust, as do true lithophile elements.Iron, meanwhile, is simplyeverywhere.
The siderophile elements include the highly siderophilicruthenium,rhodium,palladium,rhenium,osmium,iridium,platinum, andgold, the moderately siderophiliccobalt andnickel, in addition to the "disputed" elements mentioned earlier – some sources[3] even includetungsten andsilver.[5]
Most siderophile elements have practically no affinity for oxygen: indeed, oxides of gold arethermodynamically unstable. They form stronger bonds withcarbon orsulfur, but even these are not strong enough to separate out with the chalcophile elements. Thus, siderophile elements are bound with iron throughmetallic bonding in the Earth's core, where pressures may be high enough to keep the iron solid. Manganese, iron, and molybdenumdo form strong bonds with oxygen, but in the free state (as on the early Earth) can mix so easily with iron that they do not concentrate in the siliceous crust, as do true lithophile elements. However, ores of manganese are found in much the same sites as are those of aluminium and titanium, owing to manganese's great reactivity towards oxygen.
Because they are so concentrated in the dense core, siderophile elements are known for their rarity in the Earth's crust. Most of them have always been known asprecious metals because of this. Iridium is the rarest transition metal occurring within the Earth's crust, with anabundance by mass of less than one part per billion. Mineabledeposits ofprecious metals usually form as a result of theerosion ofultramafic rocks, but are not highly concentrated even compared to theircrustal abundances, which are typically several orders of magnitude below their solar abundances. However, because they are concentrated in theEarth's mantle andEarth's core, siderophile elements are believed to be present in the Earth as a whole (including the core) in something approaching their solar abundances.
The chalcophile elements (from Ancient Greek χαλκός (khalkós) 'copper, brass, bronze', also 'ore') includeAg,As,Bi,Cd,Cu,Ga,Ge,Hg,In,Pb,S,Sb,Se,Sn,Te,Tl andZn.[6]
Chalcophile elements are those that remain on or close to the surface because they combine readily withsulfur and some otherchalcogens 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 insolublesulfides.
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 theaccreting protosolar nebula when the controllingredox 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 chalcogensselenium andtellurium (which formed volatilehydrogen selenide andhydrogen 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 asplatinum).
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 andgallium 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 frombauxite, analuminum 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 byreduction, and chalcophiles' geochemical concentration – which in extreme cases can exceed 100,000 times their average crustal abundance. These greatest enrichments occur in high plateaus like theTibetan Plateau and the BolivianAltiplano where large quantities of chalcophile elements have been uplifted throughplate tectonics. A side-effect of this in modern times is that the rarest chalcophiles (likemercury) are so completely exploited that their value as minerals has almost completely disappeared.
The atmophile elements (from Ancient Greek ἀτμός (atmós) 'vapor, steam, smoke') areH,C,N and thenoble gases.[7]
Atmophile elements (also called "volatile elements") are defined as those that remain mostly on or above Earth's surface because they are, or occur in, liquids and/or gases at temperatures and pressures found on the surface. The noble gases do not form stable compounds and occur asmonatomic gases, whilenitrogen, although highly reactive as the free atom, bonds so strongly into diatomic molecular nitrogen that alloxides of nitrogen are thermodynamically unstable with respect to nitrogen and oxygen. Consequently, with thedevelopment of free oxygen in Earth's atmosphere,ammonia was oxidised to molecular nitrogen which has come to form four-fifths of the Earth's atmosphere. Carbon is also classed as an atmophile because it forms very strong multiple bonds withoxygen incarbon monoxide (slowly oxidised in the atmosphere) andcarbon dioxide. The latter is the fourth-largest constituent of the Earth's atmosphere, while carbon monoxide occurs naturally from various sources (volcanoes, combustion) and has aresidence time in the atmosphere of a few months.
Hydrogen, which occurs in water, is also classed as an atmophile. Water is classified as a volatile, because most of it is liquid or gas, even though it can exist as a solid compound at Earth's surface. Water can also be incorporated into other minerals aswater of crystallization (as ingypsum) or throughionic andhydrogen bonding (as intalc), giving hydrogen some lithophile character.
Because all atmophile elements are either gases or form volatile hydrides, atmophile elements are strongly depleted on Earth as a whole relative to their solar abundances owing to losses from the atmosphere during theformation of the Earth. The heavier noble gases (krypton,xenon) are the rarest stable elements on Earth. (In fact they, along withneon, were all first isolated and described byWilliam Ramsay andMorris Travers and assistants, who gave them names with Ancient Greek derivations of 'hidden', 'stranger', and 'new', respectively.)
Argon is the exception among the noble gases: it is the third-most abundant component ofEarth's present-day atmosphere after nitrogen and oxygen, comprisingapprox. 1%.Argon-40 is a stabledaughter of radioactive potassium-40, and argon is heavy enough to be gravitationally captured by the post-accretion Earth, so while the proto-Earth's primordial argon was mostly driven off, thisradiogenic argon has accumulated over geologic time. This makes Earth's argon abundance substantially different from cosmic abundance ratios for argon, being enormously enriched in40
Ar, while36
Ar predominates cosmically.
Synthetic elements are excluded from the classification, as they do not occur naturally.
Trace radioactive elements (namely Tc, Pm, Po, At, Rn, Fr, Ra, Ac, Pa, Np, Pu) are also treated as synthetic. Although these do occur in nature,[8][9][10] their occurrence is dependent on theirlong-lived parents Th and U, and they are not very mobile. For instance,polonium's chemistry would predict it to be a chalcophile, but it tends to occur instead as a lithophile along with its parenturanium. Evenradon, a gas atstandard conditions, does not usually have time to travel very far from the original uranium source before decaying. When needed, these elements are typically produced synthetically innuclear reactors instead of extraction from ores.