Editing Hafnium (section)

===Isotope geochemistry===
Isotopes of hafnium and [[lutetium]] (along with [[ytterbium]]) are also used in [[isotope geochemistry]] and [[geochronology|geochronological]] applications, in [[lutetium-hafnium dating]]. It is often used as a tracer of isotopic evolution of [[Mantle (geology)|Earth's mantle]] through time.<ref>{{cite journal|last1=Patchett|first1=P. Jonathan|title=Importance of the Lu-Hf isotopic system in studies of planetary chronology and chemical evolution|journal=Geochimica et Cosmochimica Acta|date=January 1983|volume=47|issue=1|pages=81–91|doi=10.1016/0016-7037(83)90092-3|bibcode=1983GeCoA..47...81P}}</ref> This is because <sup>176</sup>Lu decays to <sup>176</sup>Hf with a [[half-life]] of approximately 37 billion years.<ref>{{cite journal|last1=Söderlund|first1=Ulf|last2=Patchett|first2=P. Jonathan|last3=Vervoort|first3=Jeffrey D.|last4=Isachsen|first4=Clark E.|title=The 176Lu decay constant determined by Lu–Hf and U–Pb isotope systematics of Precambrian mafic intrusions|journal=Earth and Planetary Science Letters|date=March 2004|volume=219|issue=3–4|pages=311–324|doi=10.1016/S0012-821X(04)00012-3|bibcode=2004E&PSL.219..311S}}</ref><ref>{{cite journal|last1=Blichert-Toft|first1=Janne|author-link=Janne Blichert-Toft|last2=Albarède|first2=Francis|title=The Lu-Hf isotope geochemistry of chondrites and the evolution of the mantle-crust system|journal=Earth and Planetary Science Letters|date=April 1997|volume=148|issue=1–2|pages=243–258|doi=10.1016/S0012-821X(97)00040-X|bibcode=1997E&PSL.148..243B}}</ref><ref>{{cite journal|last1=Patchett|first1=P. J.|last2=Tatsumoto|first2=M.|title=Lu–Hf total-rock isochron for the eucrite meteorites|journal=Nature|date=11 December 1980|volume=288|issue=5791|pages=571–574|doi=10.1038/288571a0|bibcode=1980Natur.288..571P|s2cid=4284487}}</ref>

In most geologic materials, [[zircon]] is the dominant host of hafnium (>10,000 ppm) and is often the focus of hafnium studies in [[geology]].<ref>{{cite journal|last1=Kinny|first1=P. D.|title=Lu-Hf and Sm-Nd isotope systems in zircon|journal=Reviews in Mineralogy and Geochemistry|date=1 January 2003|volume=53|issue=1|pages=327–341|doi=10.2113/0530327|bibcode=2003RvMG...53..327K}}</ref> Hafnium is readily substituted into the zircon [[Crystal structure|crystal lattice]], and is therefore very resistant to hafnium mobility and contamination. Zircon also has an extremely low Lu/Hf ratio, making any correction for initial lutetium minimal. Although the Lu/Hf system can be used to calculate a "[[Nd model ages|model age]]", i.e. the time at which it was derived from a given isotopic reservoir such as the [[depleted-mantle model|depleted mantle]], these "ages" do not carry the same geologic significance as do other geochronological techniques as the results often yield isotopic mixtures and thus provide an average age of the material from which it was derived.

[[Garnet]] is another mineral that contains appreciable amounts of hafnium to act as a geochronometer. The high and variable Lu/Hf ratios found in garnet make it useful for dating [[metamorphism|metamorphic]] events.<ref>{{cite journal|last1=Albarède|first1=F.|last2=Duchêne|first2=S.|last3=Blichert-Toft|first3=J.|last4=Luais|first4=B.|last5=Télouk|first5=P.|last6=Lardeaux|first6=J.-M.|journal=Nature|title=The Lu–Hf dating of garnets and the ages of the Alpine high-pressure metamorphism|date=5 June 1997|volume=387|issue=6633|pages=586–589|doi=10.1038/42446|bibcode=1997Natur.387..586D|s2cid=4260388}}</ref>