Alunogen

(repeating unit)Al2(SO4)3·17H2OIMA symbolAlg[1]Strunz classification7.CB.45Crystal systemTriclinicCrystal classPinacoidal (1)
(same H-M symbol)Space groupP1Unit cella = 7.42, b = 26.97
c = 6.062 [Å]; α = 89.95°
β = 97.566°, γ = 91.888°; Z = 2IdentificationColourColourless; white, pale yellow to red from impuritiesCrystal habitPlaty to prismatic crystals rare, fibrous masses, crusts, and efflorescencesTwinningOn {010}CleavagePerfect on {010}, probable on {100} and {313}FractureSubconchoidalMohs scale hardness1.5–2LustreVitreous to silkyDiaphaneityTransparentSpecific gravity1.72–1.77Optical propertiesBiaxial (+)Refractive indexnα = 1.473 nβ = 1.474 nγ = 1.480Birefringenceδ = 0.0072V angleMeasured: 31 to 69°References[2][3][4]

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.[2][3]

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.[2] It occurs associated with pyrite, marcasite, halotrichite, pickeringite, epsomite, potash alum, melanterite and gypsum.[2]

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.[5][6]

References

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c d Handbook of Mineralogy
  3. ^ a b Mindat
  4. ^ Webmineral
  5. ^ "Alunogen R070601". RRUFF. Retrieved 23 August 2016.
  6. ^ "Alunogen R060015". RRUFF. Retrieved 23 August 2016.