{{Short description|Sulfate mineral}} {{For|the igneous rock type "websterite"|Websterite}} {{infobox mineral | name = Aluminite | category = Sulfate mineral | image = Aluminite - Newhaven, Sussex, England.jpg | imagesize = 260px | alt = | caption = Aluminite from Newhaven, Sussex, England | formula = Al<sub>2</sub>SO<sub>4</sub>(OH)<sub>4</sub>·7H<sub>2</sub>O |IMAsymbol=A<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.DC.05 | dana = | system = Monoclinic | class = Prismatic (2/m) <br/><small>(same H-M symbol)</small> | symmetry = ''P''2<sub>1</sub>/c | unit cell = a = 7.44, b = 15.583 <br/>c = 11.7&nbsp;[Å]; β = 110.18°; Z&nbsp;=&nbsp;4 | color = White to grayish white | colour = | habit = Needles and fibrous masses | twinning = | cleavage = None | fracture = Irregular/uneven | tenacity = Friable | mohs = 1 - 2 | luster = Dull to earthy | streak = White | diaphaneity = Translucent, opaque if massive | gravity = 1.66–1.82 | density = | polish = | opticalprop = Biaxial (+) | refractive = n<sub>α</sub> = 1.459 n<sub>β</sub> = 1.464 n<sub>γ</sub> = 1.470 | birefringence = δ = 0.011 | pleochroism = | 2V = Measured: 90°, calculated: 86° | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | references = <ref name=HBM>{{Cite web |url=http://rruff.geo.arizona.edu/doclib/hom/aluminite.pdf |title=Handbook of Mineralogy |access-date=2012-06-10 |archive-date=2012-04-26 |archive-url=https://web.archive.org/web/20120426221857/http://rruff.geo.arizona.edu/doclib/hom/aluminite.pdf |url-status=live }}</ref><ref name=Mindat>{{Cite web |url=http://www.mindat.org/min-154.html |title=Mindat w/ locations |access-date=2005-09-05 |archive-date=2009-11-09 |archive-url=https://web.archive.org/web/20091109185047/http://www.mindat.org/min-154.html |url-status=live }}</ref><ref name=Webmin>{{Cite web |url=http://webmineral.com/data/Aluminite.shtml |title=Webmineral |access-date=2005-09-05 |archive-date=2013-01-17 |archive-url=https://web.archive.org/web/20130117114225/http://webmineral.com/data/Aluminite.shtml |url-status=live }}</ref> }}

'''Aluminite''' is a hydrous aluminium sulfate mineral with formula: Al<sub>2</sub>SO<sub>4</sub>(OH)<sub>4</sub>·7H<sub>2</sub>O. It is an earthy white to gray-white monoclinic mineral which almost never exhibits crystal form. It forms botryoidal to mammillary clay-like masses. It has a very soft Mohs hardness of 1–2 and a specific gravity of 1.66–1.82. [[File:Aluminite outcrop at Newhaven Cliffs.JPG|thumb|left|An outcrop of aluminite at the top of the white chalk of the cliff at Newhaven, East Sussex, England.]]

It forms in clay and lignite deposits as an oxidation product of pyrite and marcasite along with aluminium silicates. It also occurs in volcanic sublimates, in native sulfur deposits and rarely in caves. It occurs in association with basaluminite, gibbsite, epsomite, gypsum, celestine, dolomite and goethite.<ref name=HBM/>

It was first described in 1807 from Halle, Saxony-Anhalt, Germany and named for its aluminium content.<ref name=Mindat/> It is also known as ''alley stone'', ''halite'' and ''websterite'' (named after Orcadian geologist Thomas Webster).

Aluminite is used by tile and masonry workers to reduce the setting time of mortars.{{cn|date=June 2012}}

==References== {{Reflist}}

==External links== *{{Commons category-inline}}

Category:Aluminium minerals Category:Sulfate minerals Category:Monoclinic minerals Category:Minerals in space group 14 Category:Luminescent minerals [https://www.youtube.com/watch?v=SuSQKdGFG_M Drone Video of the Outcrop at Newhaven]