Alunogen (from French ''alun'', "

alum An alum () is a type of chemical compound, usually a hydrated double salt, double sulfate salt (chemistry), salt of aluminium with the general chemical formula, formula , such that is a valence (chemistry), monovalent cation such as potassium ...

"), 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 Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

sulfate mineral The sulfate minerals are a class of minerals that include the sulfate ion () within their structure. The sulfate minerals occur commonly in primary evaporite depositional environments, as gangue minerals in hydrothermal Vein (geology), veins and as ...

. 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 Melanterite is a mineral form of hydrous iron(II) sulfate: FeSO4·7H2O. It is the iron analogue of the copper sulfate chalcanthite. It alters to siderotil by Dehydration, loss of water. It is a secondary sulfate mineral which forms from the oxida ...

and gypsum. The crystallochemical formula, can be written as: l(H₂O)₆sub>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.

References

{{Reflist Sulfate minerals Aluminium minerals Triclinic minerals Minerals in space group 2