View source for Wadsleyite

{{Short description|Mineral thought to be abundant in the Earth's mantle}}
{{multiple issues |
{{primary sources | date = July 2022}}
{{Lead too long|date=October 2024}}
}}
{{Infobox mineral|boxwidth=|boxbgcolor=|name=Wadsleyite|image=Hydrous_Fe-bearing_Wadsleyite.jpg|imagesize=176|alt=|caption=Crystal|category=[[Sorosilicate]]|formula=Mg<sub>2</sub>SiO<sub>4</sub>| IMAsymbol   = Wds<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>|strunz=9.BE.02|system=[[Orthorhombic]] (Horiuchi and Sawamoto, 1981)|class=Dipyramidal (mmm) <br/>[[H-M symbol]]: (2/m 2/m 2/m)|symmetry=''Imma''|unit cell=a = 5.7&nbsp;[[Ångström|Å]], b = 11.71&nbsp;Å <br/>c = 8.24&nbsp;Å; Z&nbsp;=&nbsp;8|molweight=|color=Dark green|habit=Microcrystalline aggregates|twinning=|cleavage=|fracture=|tenacity=|mohs=|luster=|polish=|opticalprop=Biaxial|refractive=n = 1.76|birefringence=|pleochroism=|2V=|dispersion=|extinction=|length fast/slow=|fluorescence=|absorption=|streak=|gravity=3.84 calculated|density=|melt=|fusibility=|diagnostic=|solubility=|diaphaneity=Transparent|impurities=|alteration=|other=|prop1text=|references=<ref name=Mindat>[http://www.mindat.org/min-4228.html Mindat.org]</ref><ref name=Webmin>[http://www.webmineral.com/data/Wadsleyite.shtml Webmineral data]</ref><ref name=HBM>{{cite book |editor=Anthony, John W. |editor2=Bideaux, Richard A. |editor3=Bladh, Kenneth W. |editor4=Nichols, Monte C. | orig-date = 2001 | date = 2022 | title = Handbook of Mineralogy | chapter = Wadsleyite | location = Chantilly, VA | publisher = Mineralogical Society of America | url = https://www.handbookofmineralogy.com/pdfs/wadsleyite.pdf | access-date = 5 July 2022}}</ref><ref name=IMA>[http://rruff.info/ima/# The IMA Mineral List]</ref>|colour=|prop1=}}
'''Wadsleyite''' is an [[orthorhombic]] [[mineral]] with the formula β-(Mg,Fe)<sub>2</sub>SiO<sub>4</sub>. It was first found in nature in the [[Peace River (meteorite)|Peace River]] [[meteorite]] from [[Alberta, Canada]]. It is formed by a phase transformation from [[olivine]] (α-(Mg,Fe)<sub>2</sub>SiO<sub>4</sub>) under increasing pressure and eventually transforms into [[spinel]]-structured [[ringwoodite]] (γ-(Mg,Fe)<sub>2</sub>SiO<sub>4</sub>) as pressure increases further. The structure can take up a limited amount of other bivalent [[cations]] instead of [[magnesium]], but contrary to the α and γ structures, a β structure with the sum formula Fe<sub>2</sub>SiO<sub>4</sub> is not thermodynamically stable. Its cell parameters are approximately a = 5.7&nbsp;Å, b = 11.71&nbsp;Å and c = 8.24&nbsp;Å.

Wadsleyite is found to be stable in the upper part of the Transition Zone of the Earth's [[Upper mantle|mantle]] between {{convert|410|-|520|km}} in depth. Because of oxygen atoms not bound to silicon in the Si<sub>2</sub>O<sub>7</sub> groups of wadsleyite, it leaves some oxygen atoms insufficiently bonded. Thus, these oxygens are hydrated easily, allowing for high concentrations of hydrogen atoms in the mineral. Hydrous wadsleyite is considered a potential site for water storage in the Earth's [[Mantle (geology)|mantle]] due to the low electrostatic potential of the under bonded oxygen atoms. Although wadsleyite does not contain H in its chemical formula, it may contain more than 3 percent by weight H<sub>2</sub>O, and may coexist with a hydrous melt at transition zone pressure-temperature conditions. The solubility of water and the density of wadsleyite depend on the temperature and pressure in the Earth. Even though their maximum water storage capabilities might be reduced to about 0.5–1 wt% along the normal geotherm,<ref>{{Cite journal|last1=Ohtani|first1=Eiji|last2=Litasov|first2=Konstantin|last3=Hosoya|first3=Tomofumi|last4=Kubo|first4=Tomoaki|last5=Kondo|first5=Tadashi|date=2004|title=Water transport into the deep mantle and formation of a hydrous transition zone|journal=Physics of the Earth and Planetary Interiors|volume=143–144|pages=255–269|doi=10.1016/j.pepi.2003.09.015|bibcode=2004PEPI..143..255O|issn=0031-9201}}</ref> the [[Transition zone (Earth)|transition zone]] which holds up to 60 vol% wadsleyite could still be a major water reservoir in the Earth's interior. Furthermore, the transformation resulting in wadsleyite is thought to occur also in the shock event when a meteorite impacts the Earth or another planet at very high velocity.

Wadsleyite was first identified by Ringwood and Major in 1966 and was confirmed to be a stable phase by Akimoto and Sato in 1968.<ref>{{Cite journal|last1=Akimoto|first1=Syun-iti|last2=Sato|first2=Yosiko|date=1968|title=High-pressure transformation in Co2SiO4 olivine and some geophysical implications|journal=Physics of the Earth and Planetary Interiors|language=en|volume=1|issue=7|pages=498–504|doi=10.1016/0031-9201(68)90018-6|bibcode=1968PEPI....1..498A|issn=0031-9201}}</ref> The phase was originally known as β-Mg<sub>2</sub>SiO<sub>4</sub> or "beta-phase". Wadsleyite was named for mineralogist Arthur David Wadsley (1918–1969).

== Composition ==
In values of weight percent oxide, the pure magnesian variety of wadsleyite would be 42.7% SiO<sub>2</sub> and 57.3% MgO by mass. An analysis of trace elements within wadsleyite shows a large number of elements: [[rubidium]] (Rb), [[strontium]] (Sr), [[barium]] (Ba), [[titanium]] (Ti), [[zirconium]] (Zr), [[niobium]] (Nb), [[hafnium]] (Hf), [[tantalum]] (Ta), [[thorium]] (Th), and [[uranium]] (U). This suggests that the concentrations of these elements could be larger than what has been supposed in the transition zone of Earth's upper mantle. Moreover, these results help in understanding chemical differentiation and magmatism inside the Earth.<ref>{{Cite journal|last1=Mibe|first1=Kenji|last2=Orihashi|first2=Yuji|last3=Nakai|first3=Shun'ichi|last4=Fujii|first4=Toshitsugu|date=2006|title=Element partitioning between transition-zone minerals and ultramafic melt under hydrous conditions|journal=Geophysical Research Letters|volume=33|issue=16|doi=10.1029/2006gl026999|bibcode=2006GeoRL..3316307M|issn=0094-8276|doi-access=free}}</ref>

Although nominally anhydrous, wadsleyite can incorporate more than 3 percent by weight H<sub>2</sub>O,<ref>{{Cite journal|last1=Inoue|first1=Toru|last2=Yurimoto|first2=Hisayoshi|last3=Kudoh|first3=Yasuhiro|date=1995|title=Hydrous modified spinel, Mg1.75SiH0.5O4: A new water reservoir in the mantle transition region|journal=Geophysical Research Letters|volume=22|issue=2|pages=117–120|doi=10.1029/94gl02965|bibcode=1995GeoRL..22..117I|issn=0094-8276}}</ref> which means that it is capable of incorporating more water than Earth's oceans and may be a significant reservoir for H (or water) in the Earth's interior.

== Geologic occurrence ==
Wadsleyite was found in the Peace River meteorite, an L6 [[hypersthene]]-olivine [[chondrite]] from [[Peace River]], [[Alberta, Canada]]. The wadsleyite in this meteorite is believed to have formed at high pressure during the shock event related to the impact on Earth from the olivine in sulfide-rich veins of the meteorite. It occurs as microcrystalline rock fragments, often not surpassing {{convert|0.5|mm|abbr=on}} in diameter.<ref name=":0">{{Cite journal|last=Price|first=Geoffrey D.|date=1983|title=The nature and significance of stacking faults in wadsleyite, natural β-(Mg, Fe)2SiO4 from the Peace River meteorite|journal=Physics of the Earth and Planetary Interiors|volume=33|issue=2|pages=137–147|doi=10.1016/0031-9201(83)90146-2|bibcode=1983PEPI...33..137P|issn=0031-9201}}</ref>

== Structure ==
{{multiple issues|section = yes|
{{primary sources|section| date = July 2022}}
{{Cite check|section|date=July 2022}}
{{update|section|date = July 2022}}
}}
Wadsleyite is a spinelloid, and the structure is based on a distorted cubic-closest packing of oxygen atoms as are the spinels. The a-axis and the b-axis is the half diagonal of the spinel unit. The [[magnesium]] and the [[silicon]] are completely ordered in the structure. There are three distinct octahedral sites, M1, M2, and M3, and a single tetrahedral site. Wadsleyite is a sorosilicate in which Si<sub>2</sub>O<sub>7</sub> groups are present.<ref>{{Cite journal|last1=Ashbrook|first1=Sharon E.|last2=Pollès|first2=Laurent Le|last3=Pickard|first3=Chris J.|last4=Berry|first4=Andrew J.|last5=Wimperis|first5=Stephen|last6=Farnan|first6=Ian|date=2007-03-21|title=First-principles calculations of solid-state 17O and 29Si NMR spectra of Mg2SiO4 polymorphs|url=https://pubs.rsc.org/en/content/articlelanding/2007/cp/b618211a|journal=Physical Chemistry Chemical Physics|language=en|volume=9|issue=13|pages=1587–1598|doi=10.1039/B618211A|pmid=17429552|bibcode=2007PCCP....9.1587A|issn=1463-9084 | url-access=subscription}}</ref>{{better source|date = July 2022}} There are four distinct oxygen atoms in the structure. O2 is a bridging oxygen shared between two tetrahedra, and O1 is a non-silicate oxygen (not bonded to Si). The potentially hydrated O1 atom lies at the center of four edge-sharing Mg<sup>2+</sup> [[octahedra]].<ref>{{Cite journal|last=Smyth|first=Joseph R.|date=1987-12-01|title=beta -Mg2 SiO4; a potential host for water in the mantle?|url=https://pubs.geoscienceworld.org/msa/ammin/article-abstract/72/11-12/1051/41947/beta-Mg2-SiO4-a-potential-host-for-water-in-the|journal=American Mineralogist|language=en|volume=72|issue=11–12|pages=1051–1055|issn=0003-004X | url-access=subscription}}</ref><ref>{{Cite journal|last=Smyth|first=Joseph R.|date=1994-10-01|title=A crystallographic model for hydrous wadsleyite (β-Mg2SiO4): An ocean in the Earth's interior?|url=https://pubs.geoscienceworld.org/msa/ammin/article-abstract/79/9-10/1021/42912/A-crystallographic-model-for-hydrous-wadsleyite|journal=American Mineralogist|language=en|volume=79|issue=9–10|pages=1021–1024|issn=0003-004X | url-access=subscription}}</ref>{{primary source inline|date = July 2022}} If this oxygen is hydrated (protonated), a Mg vacancy can occur at M3. If water incorporation exceeds about 1.5% the M3 vacancies can be ordered in violation of space group ''Imma'', reducing the symmetry to monoclinic ''I''2/''m'' with beta angle up to 90.4º.{{fact|date = July 2022}}

Wadsleyite II is a separate spinelloid phase with both a single (SiO<sub>4</sub>) and double (Si<sub>2</sub>O<sub>7</sub>) tetrahedral units. It is a magnesium-iron [[silicate]] with variable composition that might occur between the stability regions of wadsleyite and [[ringwoodite]] γ-Mg<sub>2</sub>SiO<sub>4</sub>,<ref>{{Cite journal|last=Kleppe|first=A. K.|date=2006|title=High-pressure Raman spectroscopic studies of hydrous wadsleyite II|journal=American Mineralogist|volume=91|issue=7|pages=1102–1109|doi=10.2138/am.2006.2060|bibcode=2006AmMin..91.1102K|s2cid=51496930|issn=0003-004X}}</ref> but computational models suggest that at least the pure magnesian form is not stable.<ref>{{Cite journal|last1=Tokár|first1=Kamil|last2=Jochym|first2=Paweł T.|last3=Piekarz|first3=Przemysław|last4=Łażewski|first4=Jan|last5=Sternik|first5=Małgorzata|last6=Parlinski|first6=Krzysztof|date=2013|title=Thermodynamic properties and phase stability of wadsleyite II|journal=Physics and Chemistry of Minerals|language=en|volume=40|issue=3|pages=251–257|doi=10.1007/s00269-013-0565-9|bibcode=2013PCM....40..251T|issn=0342-1791|doi-access=free}}</ref> One-fifth of the silicon atom is in isolated tetrahedral and four-fifths is in Si<sub>2</sub>O<sub>7</sub> groups so that the structure can be thought of as a mixture of one-fifth spinel and four-fifths wadsleyite.<ref name=":1">{{Cite journal|last1=Horiuchi|first1=Hiroyuki|last2=Sawamoto|first2=Hiroshi|date=1981|title=β-Mg2SiO4: Single-crystal X-ray diffraction study|url=https://pubs.geoscienceworld.org/msa/ammin/article-abstract/66/5-6/568/41286/Mg2SiO4-Single-crystal-X-ray-diffraction-study|journal=American Mineralogist|language=en|volume=66|issue=5–6|pages=568–575|issn=0003-004X| url-access=subscription}}</ref>{{primary source inline|date = July 2022}}

== Crystallography and physical properties ==
[[File:Mg-wadsleyite-pV.svg|thumb|upright=1.5|Molar volume vs. pressure at room temperature]]
Wadsleyite crystallizes in the [[orthorhombic]] crystal system and has a unit cell volume of 550.00&nbsp;Å<sup>3</sup>. Its space group is ''Imma'' and its cell parameters are a = 5.6921&nbsp;[[Angstrom|Å]], b = 11.46&nbsp;Å and c = 8.253&nbsp;Å;<ref name=":0" /> an independent study found the cell parameters to be a = 5.698&nbsp;Å, b = 11.438&nbsp;Å and c = 8.257&nbsp;Å.<ref name=":1" /> Pure magnesian wadsleyite is colorless, but iron-bearing varieties are dark green.

The wadsleyite minerals generally have a [[microcrystalline]] texture and are fractured. Because of small crystal size, detailed [[optical]] data could not be obtained; however, wadsleyite is [[anisotropic]] with low first-order [[birefringence]] colors.<ref name=":0" /> It is biaxial with a mean [[refractive index]] of n = 1.76 and has a calculated [[specific gravity]] of 3.84. In X-ray [[powder diffraction]], its strongest points in pattern are: 2.886(50)(040), 2.691(40)(013), 2.452(100,141), 2.038(80)(240), 1.442(80)(244).<ref name=":0" />

== Sound velocities ==
Sawamoto et al. (1984) <ref name=":2">{{Cite journal|last1=SAWAMOTO|first1=H.|last2=WEIDNER|first2=D. J.|last3=SASAKI|first3=S.|last4=KUMAZAWA|first4=M.|date=1984|title=Single-Crystal Elastic Properties of the Modified Spinel (Beta) Phase of Magnesium Orthosilicate|journal=Science|volume=224|issue=4650|pages=749–751|doi=10.1126/science.224.4650.749|pmid=17780624|bibcode=1984Sci...224..749S|s2cid=6602306|issn=0036-8075}}</ref> firstly measured the [[P-wave]] velocity (Vp) and [[S-wave]] velocity (Vs) of Mg-endmember of wadsleyite at ambient condition by the [[Brillouin spectroscopy]]. Their data suggested that olivine-wadsleyite phase transition would cause a Vp jump of ~13% and a Vs jump of ~14%. Therefore, the olivine-wadsleyite phase transition has been suggested as the main reason for the 410&nbsp;km seismic discontinuity at the boundary between the [[Upper mantle (Earth)|Upper Mantle]] and the [[Transition zone (Earth)|Mantle Transition Zone]] in Earth.<ref name=":2" />

== Namesake ==
Arthur David Wadsley (1918–1969) received the privilege of getting a mineral named after him due to his contributions to geology such as the [[crystallography]] of minerals and other [[inorganic compounds]].<ref name=":0" /> The proposal to have wadsleyite named after Wadsley was approved by the Commission on New Minerals and Mineral Names of the [[International Mineralogical Association]]. The type specimen is now preserved in the collection of the Department of Geology at the [[University of Alberta]].

==See also==
* [[Glossary of meteoritics]]

== References ==
{{Reflist}}
<references group="" responsive="1"></references>
{{Refbegin|}}{{Refend}}

{{Meteorites}}

[[Category:Sorosilicates]]
[[Category:Meteorite minerals]]
[[Category:Orthorhombic minerals]]
[[Category:Minerals in space group 74]]