{{Short description|Aluminium sulfate mineral}} {{Infobox mineral | name = Alunogen | boxwidth = | boxbgcolor = | image = Alunogen - Almyras, Agia Varvara, Cyprus.jpg | imagesize = | alt = | caption = Alunogen | category = Sulfate minerals | formula = Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>·17H<sub>2</sub>O |IMAsymbol=Alg<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 = 7.CB.45 | dana = | system = Triclinic | class = Pinacoidal ({{overline|1}}) <br/><small>(same H-M symbol)</small> | symmetry = ''P''{{overline|1}} | unit cell = a = 7.42, b = 26.97 <br/>c = 6.062 [Å]; α = 89.95° <br/>β = 97.566°, γ = 91.888°; Z = 2 | colour = Colourless; white, pale yellow to red from impurities | habit = Platy to prismatic crystals rare, fibrous masses, crusts, and efflorescences | twinning = On {{mset|010}} | cleavage = Perfect on {{mset|010}}, probable on {{mset|100}} and {{mset|{{overline|31}}3}} | fracture = Subconchoidal | tenacity = | mohs = 1.5–2 | lustre = Vitreous to silky | streak = | diaphaneity = Transparent | gravity = 1.72–1.77 | density = | polish = | opticalprop = Biaxial (+) | refractive = n<sub>α</sub> = 1.473 n<sub>β</sub> = 1.474 n<sub>γ</sub> = 1.480 | birefringence = δ = 0.007 | pleochroism = | 2V = Measured: 31 to 69° | references = <ref name=HBM>[http://rruff.info/doclib/hom/alunogen.pdf Handbook of Mineralogy]</ref><ref name=Mindat>[http://www.mindat.org/min-162.html Mindat]</ref><ref name=Webmin>[http://webmineral.com/data/Alunogen.shtml Webmineral]</ref> }} '''Alunogen''' (from French ''alun'', "alum"), also called '''feather alum''' and '''hair salt''' is a colourless to white (although often coloured by impurities, such as iron substituting for aluminium) fibrous to needle-like aluminium sulfate mineral. It has the chemical formula Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>·17H<sub>2</sub>O.<ref name=HBM/><ref name=Mindat/>
It is often found on the walls of mines and quarries as a secondary mineral. It can be found in the oxidation zones of some ore deposits as well as on burning coal dumps (i.e., as the product of millosevichite hydration). It also forms as a low temperature deposit in fumaroles.<ref name=HBM/> It occurs associated with pyrite, marcasite, halotrichite, pickeringite, epsomite, potash alum, melanterite and gypsum.<ref name=HBM/>
The crystallochemical formula, can be written as: [Al(H<sub>2</sub>O)<sub>6</sub>]<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub><sup>.</sup>5H<sub>2</sub>O. The second formula shows that H<sub>2</sub>O in the alunogen formula occurs both as ligand (coordinative form) and loosely bound (crystallization) form.<ref>{{Cite web|url=http://rruff.info/alunogen/display=default/R070601|title=Alunogen R070601|last=|first=|date=|website=RRUFF|publisher=|access-date=23 August 2016}}</ref><ref>{{Cite web|url=http://rruff.info/alunogen/display=default/R060015|title=Alunogen R060015|last=|first=|date=|website=RRUFF|publisher=|access-date=23 August 2016}}</ref>
==References== {{Reflist}}
Category:Sulfate minerals Category:Aluminium minerals Category:Triclinic minerals Category:Minerals in space group 2