alunogen

{{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 = Al₂(SO₄)₃·17H₂O

|IMAsymbol=Alg{{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}}

| molweight =

| strunz = 7.CB.45

| dana =

| system = Triclinic

| class = Pinacoidal ({{overline|1}})
(same H-M symbol)

| symmetry = P{{overline|1}}

| unit cell = a = 7.42, b = 26.97
c = 6.062 [Å]; α = 89.95°
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_α = 1.473 n_β = 1.474 n_γ = 1.480

| birefringence = δ = 0.007

| pleochroism =

| 2V = Measured: 31 to 69°

| references = [http://rruff.info/doclib/hom/alunogen.pdf Handbook of Mineralogy][http://www.mindat.org/min-162.html Mindat][http://webmineral.com/data/Alunogen.shtml Webmineral]

}}

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 Al₂(SO₄)₃·17H₂O.

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. It occurs associated with pyrite, marcasite, halotrichite, pickeringite, epsomite, potash alum, melanterite and gypsum.

The crystallochemical formula, can be written as: [Al(H₂O)₆]₂(SO₄)₃^.5H₂O. The second formula shows that H₂O in the alunogen formula occurs both as ligand (coordinative form) and loosely bound (crystallization) form.{{Cite web|url=http://rruff.info/alunogen/display=default/R070601|title=Alunogen R070601|last=|first=|date=|website=RRUFF|publisher=|access-date=23 August 2016}}{{Cite web|url=http://rruff.info/alunogen/display=default/R060015|title=Alunogen R060015|last=|first=|date=|website=RRUFF|publisher=|access-date=23 August 2016}}