Editing Coffinite

{{Short description|Uranium-bearing silicate mineral}}
{{Infobox mineral
| name        = Coffinite
| category    = [[Silicate minerals|Nesosilicate]]
| boxwidth    = 
| boxbgcolor  =#b46d4e 
| boxtextcolor = #fff
| image       = Blenda smolista + coffinit.jpg
| imagesize   = 260px
| alt         = 
| caption     = [[Uraninite|Pitchblende]] and coffinite in a sample from a Czech mine
| formula     = U(SiO<sub>4</sub>)<sub>1−x</sub>(OH)<sub>4x</sub>
| IMAsymbol=Cof<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|url=https://www.cambridge.org/core/journals/mineralogical-magazine/article/imacnmnc-approved-mineral-symbols/62311F45ED37831D78603C6E6B25EE0A|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>  
| molweight   = 
| strunz      = 9.AD.30
| dana        =
| system      = [[Tetragonal]]
| class       = Ditetragonal dipyramidal (4/mmm) <br/>[[H-M symbol]]: (4/m 2/m 2/m)
| symmetry    = ''I''4<sub>1</sub>/amd
| unit cell   = a = 6.97&nbsp;Å, c = 6.25&nbsp;Å; Z&nbsp;=&nbsp;4
| color       = Black (from organic inclusions; pale to dark brown in [[thin section]]
| colour      = 
| habit       = Rarely as crystals, commonly as colloform to botryoidal incrustations, fibrous, pulverulent masses
| twinning    = 
| cleavage    = 
| fracture    = Irregular to subconchoidal
| tenacity    = Brittle to friable
| mohs        = 5–6
| luster      = Dull to adamantine
| streak      = Grayish black
| diaphaneity = Opaque, transparent on thin edges
| gravity     = 5.1
| density     = 
| polish      = 
| opticalprop = Uniaxial (+/−)
| refractive  = n<sub>α</sub> = 1.730–1.750 n<sub>β</sub> = 1.730–1.750
| birefringence = δ = 1.730
| pleochroism = Moderate; pale yellow-brown parallel to and medium brown perpendicular to long axis
| 2V          = 
| dispersion  = 
| extinction  = 
| length fast/slow =
| fluorescence= 
| absorption  =
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| other       = [[Image:Radioactive.svg|25px]] [[Radioactive]]
72.63% (U)
| alteration  = [[Metamict]]
| references  = <ref>[https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Coffinite Mineralienatlas]</ref><ref name=HBM>{{cite web |last1=Anthony |first1=John W. |last2=Bideaux |first2=Richard A. |last3=Bladh |first3=Kenneth W. |last4=Nichols |first4=Monte C. |title=Coffinite |url=http://www.handbookofmineralogy.org/pdfs/coffinite.pdf |website=Handbook of Mineralogy |publisher=Mineral Data Publishing |access-date=19 June 2022 |date=2005}}</ref><ref name=Webmin>[http://webmineral.com/data/Coffinite.shtml Webmineral data]</ref><ref name=Mindat>{{mindat|id=1106|title=Coffinite}}</ref><ref name=Stieff55>{{cite journal | last1 = Stieff | first1 = L.R. | last2 = Stern | first2 = T.W | last3 = Sherwood | first3 = A.M. | year = 1955 | title = Preliminary Description of Coffinite – A New Uranium Mineral | journal = Science | volume = 121 | issue = 3147 | pages = 608–609 | doi=10.1126/science.121.3147.608-a| bibcode = 1955Sci...121..608S | hdl = 2027/mdp.39015095016906 | hdl-access = free }}</ref><ref name=Fuchs58>{{cite journal | last1 = Fuchs | first1 = L.H. | last2 = Gebert | first2 = E. | year = 1958 | title = X-Ray Studies of Synthetic Coffinite, Thorite and Uranothorites | journal = American Mineralogist | volume = 43 | pages = 243–248 }}</ref><ref name=Stieff56>{{cite journal | last1 = Stieff | first1 = L.R. | last2 = Stern | first2 = T.W | last3 = Sherwood | first3 = A.M. | year = 1956 | title = Coffinite, a Uranous Silicate with Hydroxyl Substitution – A New Mineral | journal = American Mineralogist | volume = 41 | pages = 675–688 }}</ref><ref name=Hansley89>{{cite journal | last1 = Hansley | first1 = P.L. | last2 = Fitzpatrick | first2 = J.J. | year = 1989 | title = Compositional and Crystallographic Data on REE-Bearing Coffinite from the Grants Uranium Region, Northwestern New-Mexico | journal = American Mineralogist | volume = 74 | pages = 263–270 }}</ref><ref name=Moench62>{{cite journal | last1 = Moench | first1 = R.H. | year = 1962 | title = Properties and Paragenesis af Coffinite from Woodrow Mine, New Mexico | journal = American Mineralogist | volume = 47 | pages = 26–33 }}</ref><ref name=Min05>{{cite journal | last1 = Min | first1 = M.Z. | last2 = Fang | first2 = C.Q. | last3 = Fayek | first3 = M. | year = 2005 | title = Petrography and Genetic History of Coffinite and Uraninite from the Liueryiqi Granite-Hosted Uranium Deposit, SE China | journal = Ore Geology Reviews | volume = 26 | issue = 3–4 | pages = 187–197 | doi=10.1016/j.oregeorev.2004.10.006}}</ref><ref name=Zhang09>{{cite journal | last1 = Zhang | first1 = F. X. | last2 = Pointeau | first2 = V. | last3 = Shuller | first3 = L. C. |display-authors=et al | year = 2009 | title = Response of Synthetic Coffinite to Energetic Ion Beam Irradiation | journal = American Mineralogist | volume = 94 | pages = 916–920 | doi = 10.2138/am.2009.3111 | s2cid = 73581946 }}</ref><ref name=Hoekstra56>{{cite journal | last1 = Hoekstra | first1 = H.R. | last2 = Fuchs | first2 = L.H. | year = 1956 | title = Synthesis of Coffinite-USiO4 | journal = Science | volume = 123 | issue = 3186 | pages = 105 | doi=10.1126/science.123.3186.105| bibcode = 1956Sci...123..105H }}</ref><ref name=pnas15>{{cite journal|author1=Guo X. |author2=Szenknect S. |author3=Mesbah A. |author4=Labs S. |author5=Clavier N. |author6=Poinssot C. |author7=Ushakov S.V. |author8=Curtius H. |author9=Bosbach D. |author10=Rodney R.C. |author11=Burns P. |author12=Navrotsky A. |title= Thermodynamics of Formation of Coffinite, USiO4|journal= Proc. Natl. Acad. Sci. USA|year= 2015|volume= 112|issue= 21|pages= 6551–6555| doi= 10.1073/pnas.1507441112 |pmid=25964321 |pmc=4450415
|bibcode=2015PNAS..112.6551G |doi-access=free }}</ref>
}}
'''Coffinite''' is a [[uranium]]-bearing [[silicate mineral]] with formula: U(SiO<sub>4</sub>)<sub>1−x</sub>(OH)<sub>4x</sub>.

It occurs as black incrustations, dark to pale-brown in [[thin section]]. It has a grayish-black streak. It has a brittle to conchoidal [[fracture]]. The hardness of coffinite is between 5 and 6.

It was first described in 1954 for an occurrence at the La Sal No. 2 Mine, Beaver Mesa, [[Mesa County, Colorado]], US,<ref name=Mindat/> and named for American geologist [[Reuben Clare Coffin]] (1886–1972).<ref name=HBM/>
It has widespread global occurrence in [[Colorado Plateau]]-type [[uranium ore deposits]] of uranium and [[vanadium]]. It replaces organic matter in [[sandstone]] and in [[hydrothermal vein]] type deposits.<ref name=HBM/> It occurs in association with [[uraninite]], [[thorite]], [[pyrite]], [[marcasite]], [[roscoelite]], [[clay mineral]]s and [[amorphous]] [[organic matter]].<ref name=HBM/>

==Composition==
Coffinite's chemical formula is U(SiO<sub>4</sub>)<sub>1−x</sub>(OH)<sub>4x</sub>.<ref name=Stieff55 /><ref name=":0">{{Cite journal |last1=Jackson |first1=Robert A. |last2=Montenari |first2=Michael |date=2019 |title=Computer modeling of Zircon (ZrSiO4)—Coffinite (USiO4) solid solutions and lead incorporation: Geological implications |url=https://www.sciencedirect.com/science/article/abs/pii/S246851781930005X |journal=Stratigraphy & Timescales |volume=4 |pages=217–227 |doi=10.1016/bs.sats.2019.08.005 |isbn=9780128175521 |s2cid=210256739 |via=Elsevier Science Direct|url-access=subscription }}</ref>  X-ray powder patterns from samples of coffinite allowed geologists to classify it as a new mineral in 1955.<ref name=Stieff55 />  A comparison to the x-ray powder pattern of [[zircon]] (ZrSiO<sub>4</sub>) and thorite (ThSiO<sub>4</sub>) was the basis for this classification.<ref name=Fuchs58/>  Preliminary chemical analysis indicated that the uranous silicate exhibited hydroxyl substitution.<ref name=Fuchs58/>  The results of Sherwood's preliminary chemical analysis were based on samples from three locations.  Hydroxyl bonds and silicon-oxygen bonds also proved to exist after infrared absorption spectral analyses were performed.<ref name=Stieff56/>  The hydroxyl substitution occurs as (OH)<sub>4</sub><sup>4−</sup> for (SiO<sub>4</sub>)<sup>4−</sup>.<ref name=Stieff56/>  The hydroxyl constituent in coffinite later proved to be nonessential in the formation of a stable synthetic mineral.<ref name=Hansley89/>  Recent [[electron microprobe]] analysis of the submicroscopic crystals uncovered an abundance of [[calcium]], [[yttrium]], [[phosphorus]], and minimal lead substitutions along with traces of other rare earth elements.<ref name=Hansley89/>

==Crystal structure==
Coffinite is [[isostructural]] with the orthosilicates zircon (ZrSiO<sub>4</sub>) and thorite (ThSiO<sub>4</sub>).<ref>{{cite journal | last1 = Pointeau | first1 = V. |display-authors=et al | year = 2009 | title = Synthesis and Characterization of Coffinite | journal = Journal of Nuclear Materials | volume = 393 | issue = 3 | pages = 449–458 | doi=10.1016/j.jnucmat.2009.06.030| bibcode = 2009JNuM..393..449P }}</ref>  Stieff et al. analyzed coffinite using the x-ray powder diffraction technique and determined that it has a tetragonal structure.<ref name=Stieff56/>  Occurring naturally with U<sup>4+</sup> cations, the UO<sub>8</sub> triangular dodecahedra coordinate with edge-sharing, alternating SiO<sub>4</sub> [[tetrahedra]] in chains along the c-axis.<ref name=Zhang09/>  The central uranium site of coffinite is surrounded by eight SiO<sub>4</sub> tetrahedra.  The lattice dimensions of naturally-occurring and synthetic coffinite are similar, with a naturally-occurring sample from Arrowhead Mine, Mesa County, Colorado having a=6.93kx, c=6.30kx, and a sample synthesized by Hoekstra and Fuchs having a=6.977kx and c=6.307kx.<ref name=":0" /><ref name=Hoekstra56/>

==Physical properties==
Initial examination of coffinite by Stieff et al. described the mineral as black in color with an adamantine luster, indistinguishable from [[uraninite]] (UO<sub>2</sub>).<ref name=Stieff56/>  Additionally, the discoverers reported that although no cleavage is seen in coffinite, it does exhibit subconchoidal fracturing and is very fine grained.  Initial samples showed a brittle texture and a hardness between 5 and 6, with a specific gravity of 5.1.<ref name=Stieff56/>  Later samples from Woodrow Mine in New Mexico collected by Moench showed fibrous internal structure and exceptional crystallization.<ref name=Moench62/>  A polished thin section of coffinite has a brown color and shows anisotropic transmission of light.<ref name=Moench62/>  Optical analysis yielded a refractive index of about 1.74.<ref name=Moench62/>

==Geological occurrence==
Coffinite was first discovered in sedimentary uranium deposits in the Colorado Plateau region,<ref name=Min05/> but has also been discovered in sedimentary uranium deposits and hydrothermal veins in many other locations.<ref name=Hansley89/>  Samples of coffinite from the Colorado Plateau were found with black fine-grained low-valence [[vanadium]] minerals, uraninite and finely dispersed black organic material.<ref name=":0" /><ref name=Stieff56/>  Other materials associated with later finds from the same region were [[clay]] and [[quartz]].<ref name=Min05/>  In vein deposits of the Copper King Mine in Colorado, coffinite was also found to occur with [[uraninite]] and [[pitchblende]].<ref name=Stieff56/>  Coffinite is metastable<ref name=pnas15/> compared to [[uraninite]] and [[quartz]], thus formation of coffinite requires a [[uranium]] source in [[Redox|reducing conditions]], as evidenced by the associated presence of low-valence vanadium minerals.<ref name=Stieff56/>  Silica-rich solution provides such a reducing condition in cases where coffinite results as an alteration product of [[uraninite]].<ref name=Zhang09/>  Hansley and Fitzpatrick also noted that the brownish color of their coffinite samples was caused by organic material, leading them to conclude that coffinite can also form in low temperature conditions if organic carbon is present.<ref name=Hansley89/>  This finding is consistent with the coffinite samples of the Colorado Plateau, which included fossilized wood.<ref name=Min05/>  In China, coffinite can be found in [[granite]] in addition to [[sandstone]].<ref name=Min05/>  Hansley and Fitzpatrick concluded that coarse-grained coffinite most likely forms in high temperature environments.<ref name=Hansley89/>  Coffinite and uraninite precipitate inside brecciated and fractured regions of altered granite at pressures between 500 and 800&nbsp;bars and temperatures at 126 to 178&nbsp;°C.<ref name=Min05/>

==Special characteristics==
A large percentage of the Earth's uranium supply is contained in coffinite deposits,<ref>Deditius, Arthur P., Utsunomiya, Satoshi, Ewing, Rodney C. (2008) The Chemical Stability of Coffinite, USiO4 Center Dot NH(2)O; 0 < N < 2, Associated With Organic Matter: A Case Study from Grants Uranium Region, New Mexico, USA. ''Chemical Geology'', 251, 33-49.</ref> which is significant because of uranium's use in nuclear energy.  Sedimentary deposits contain the most radioactive samples,<ref name=Stieff56/> as evidenced by the intensely radioactive coffinite found in the Colorado Plateau.<ref name=Stieff55 />   Researchers at [[Harvard University]], the [[United States Geological Survey]] (USGS), and several other institutions attempted unsuccessfully to synthesize coffinite in the mid-1950s after its initial discovery.<ref name=Stieff55 />  In 1956, Hoekstra and Fuchs managed to create stable samples of synthetic coffinite.  All of this research was conducted for the [[United States Atomic Energy Commission]].<ref name=Hoekstra56/>

==References==
{{Reflist}}

{{Commons category}}

[[Category:Uranium(IV) minerals]]
[[Category:Nesosilicates]]
[[Category:Tetragonal minerals]]
[[Category:Minerals in space group 141]]