Huemulite

{{Short description|Mineral}} {{Infobox mineral | name = Huemulite | category = Oxide mineral | boxwidth = | boxbgcolor = | image = Huemulite.jpg | imagesize = | caption = | formula = Na₄Mg(V₁₀O₂₈)·24H₂O | IMAsymbol = Hml<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> | molweight = | strunz = 4.HG.10 | dana = 47.2.3.1 | system = Triclinic | symmetry = P{{overline|1}} (no. 2) | unit cell = a = 9.0453(2)&nbsp;Å <br/>b = 11.3337(3)&nbsp;Å <br/>c = 11.7372(8)&nbsp;Å <br/>α = 105.223(7)° <br/>β = 97.383(7)° <br/>γ = 100.790(7)°; Z&nbsp;=&nbsp;1<ref name=C849/> | color = Yellowish orange to orange | habit = | twinning = | cleavage = | fracture = | tenacity = | mohs = 2.5 to 3 | luster = Dull | polish = | refractive = n_α = 1.679(3)<br>n_β = 1.734(3)<br>n_γ = 1.742(2) | opticalprop = Biaxial (-) | birefringence = δ = 0.063 | 2V = 25° to 30° (measured) | dispersion = r > v strong | pleochroism = Visible | fluorescence= Not fluorescent<ref name=G1/> | absorption = | streak = Yellow | gravity = 2.39 g/cm³<ref name=G1/> | density = | melt = {{convert|500|C|F}}<ref name=G12>Gordillo, p. 12.</ref> | fusibility = | diagnostic = | solubility = Soluble in water | diaphaneity = Translucent | other = | references =<ref name=mindat>{{cite web|title=Huemulite|url=http://www.mindat.org/min-1941.html|publisher=Mindat|accessdate=July 26, 2012}}</ref><ref name=atlas>[https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Huemulite Mineralienatlas]</ref><ref>{{cite journal |last1=Colombo |first1=F. |last2=Baggio |first2=R. |last3=Kampf |first3=A. R. |title=The Crystal Structure of the Elusive Huemulite |journal=The Canadian Mineralogist |date=1 June 2011 |volume=49 |issue=3 |pages=849–864 |doi=10.3749/canmin.49.3.849|bibcode=2011CaMin..49..849C |hdl=11336/53388 |hdl-access=free }}</ref> }} '''Huemulite''' is a mineral with formula Na₄Mg(V₁₀O₂₈)·24H₂O that is yellow to orange in color. It was first discovered in Argentina in 1959 and described in 1966.<ref>{{Cite web |title=Huemulite Mineral Data |url=https://www.webmineral.com/data/Huemulite.shtml |access-date=2024-06-05 |website=www.webmineral.com}}</ref> The mineral is named for the Huemul mine in which it was discovered.

==Occurrence and properties== Huemulite is yellowish orange to orange and bright in color.<ref name=handbook/><ref name=G3/> The mineral occurs as thin films, aggregates of fine fibers, botryoidal masses, and interstitial filling in host sandstone.<ref name=G1/><ref name=handbook/> Huemulite has been found in Argentina, the Czech Republic, the United Kingdom, and the United States.<ref name=mindat/> It occurs in association with epsomite, gypsum, hummerite, rossite, and thenardite.<ref name=handbook>{{cite web|title=Huemulite|url=http://www.handbookofmineralogy.com/pdfs/huemulite.pdf|work=Handbook of Mineralogy|publisher=Mineral Data Publishing|accessdate=July 26, 2012|archive-date=July 16, 2012|archive-url=https://web.archive.org/web/20120716013128/http://www.handbookofmineralogy.com/pdfs/huemulite.pdf|url-status=dead}}</ref>

Huemulite is a member of the pascoite group.<ref name=mindat/> It melts at {{convert|500|C|F}} to become a red liquid. Huemulite dissolves readily in cold water to produce an orange-yellow solution with a pH of 5.5 to 6.5.<ref name=G12>Gordillo, p. 12.</ref>

==Formation and synthesis== In Argentina, the mineral formed after mine tunnels were cut through Cu-U deposits in sandstone and conglomerate.<ref name=handbook/><ref name=G3>Gordillo, p. 3.</ref> The vanadium in huemulite is thought to originate from asphaltic material that occurs in association with the sandstone.<ref name=G3/>

Huemulite can be synthesized by mixing stoichiometric proportions of vanadium pentoxide, magnesium carbonate, and sodium carbonate in cold water in a humid environment. The mixture is heated to dissolve the compounds which react with each other as CO₂ is drawn off. The solution is then concentrated, excess vanadic acid is removed by filtration, and allowed to cool and crystallize.<ref name=G12/>

Since huemulite dissolves easily in water, it can be recrystallized by evaporating the mineral solution.<ref name=G2/> When evaporated slowly, the process creates well-formed crystals up to {{convert|5|mm|in|abbr=on}} and {{convert|15|to|25|mg|oz|abbr=on}}. In a more humid environment, fibrous crystals or acicular radial aggregates are formed.<ref name=G12/>

Both recrystallized and synthetic huemulite have tabular habit.<ref name=G5/>

==Structure== Huemulite exhibits the triclinic crystal system with space group P{{overbar|1}} and one formula unit per unit cell.<ref name=C857/> The crystal structure consists of decavanadate anions (V₁₀O₂₈)⁶⁻ linked by an interstitial complex of isolated [Mg(H₂O)₆]²⁺ and an infinite zigzag chain of [Na₄(H₂O)₁₄]⁴⁺. There are a further four isolated H₂O groups, two of which are positionally disordered.<ref name=C849>Colombo, p. 849.</ref>

==History== Huemulite was discovered in the area of Malargüe in Mendoza Province, Argentina.<ref name=G3/> The first specimen was collected in 1959 by V. Angelelli of the Geology Department of CNEA on level -18 of the Agua Botada ore body. The specimen was sent to E. Linares who determined it to be unlike any known mineral.<ref name=G2>Gordillo, p. 2.</ref> Further specimens were collected in the mine as well as the nearby Huemul and Agua Botada Sur mines.<ref name=G2_3>Gordillo, pp. 2–3.</ref> In 1963, a preliminary report on the mineral was presented to the II Argentine Geological Congress. In 1964, the unit cell was measured at Yale University by Linares and H. Winchell and the mineral's chemical and physical properties were checked by C. E. Gordillo and R. O. Toubes.<ref name=G2/> The mineral was named ''huemulite'' after the Huemul mine in which it was discovered. On May 19, 1965, the mineral and name were approved by the Commission on New Minerals and Mineral Names of the IMA. Huemulite was described in 1966 in the journal ''American Mineralogist'' by Gordillo, Linares, Toubes, and Winchell.<ref name=G1>Gordillo, p. 1.</ref>

Synthetic huemulite was deposited by Gordillo in the Museo de Mineralogía of the Universidad Nacional de Córdoba.<ref name=C850>Colombo, p. 850.</ref> No type specimens were designated by them, however, a type specimen was donated by Linares to the National Museum of Natural History in Washington, D.C. Unfortunately, during a 2011 study, the only mineral detected similar to huemulite was lasalite.<ref name=C855>Colombo, p. 855.</ref> It was determined that Gordillo ''et al.'' most likely used fully hydrated huemulite in chemical analysis and partially dehydrated huemulite in determining the mineral's powder X-ray diffraction.<ref name=C857>Colombo, p. 857.</ref>

==Analysis== Huemulite in its natural form is too fine-grained for accurate study of its physical and optical properties;<ref name=G4_5>Gordillo, pp. 4–5.</ref> however, it can readily be recrystallized after dissolving the mineral in water. As far as can be determined, both recrystallized and synthetic huemulite are identical to natural specimens.<ref name=G5>Gordillo, p. 5.</ref>

==References== {{Reflist|30em}}

;Bibliography *{{cite journal|last1=Colombo|first1=Fernando|last2=Baggio|first2=Ricardo|last3=Kampf|first3=Anthony R.|title=The crystal structure of the elusive huemulite|journal=The Canadian Mineralogist|date=June 2011|volume=49|issue=3|pages=849–864|doi=10.3749/canmin.49.3.849|bibcode=2011CaMin..49..849C |hdl=11336/53388|hdl-access=free}} {{subscription required}} *{{cite journal|last1=Gordillo|first1=C. E.|last2=Linares|first2=E.|last3=Toubes|first3=R. O.|last4=Winchell|first4=H.|title=Huemulite, Na₄MgV₁₀O₂₈·24H₂O, a new hydrous sodium and magnesium vanadate from Huemul Mine, Mendoza Province, Argentina|journal=American Mineralogist|date=January–February 1966|volume=51|issue=1 & 2|pages=1–13|url=http://www.minsocam.org/ammin/AM51/AM51_1.pdf}}

==External links== *[http://www.mindat.org/gallery.php?min=1941 Photos of huemulite] from mindat.org

Category:Triclinic minerals Category:Sodium minerals Category:Magnesium minerals Category:Vanadate minerals 24 Category:Minerals in space group 2