Alunogen (from French ''alun'', “

alum An alum () is a type of chemical compound, usually a hydrated double sulfate salt of aluminium with the general formula , where is a monovalent cation such as potassium or ammonium. By itself, "alum" often refers to potassium alum, with the ...

”), 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 (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It 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 veins and as secondary ...

. 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 Millosevichite is a rare sulfate mineral with the chemical formula Al2(SO4)3. Aluminium is often substituted by iron. It forms finely crystalline and often porous masses. It was first described in 1913 for an occurrence in Grotta dell'Allume, Por ...

hydration). It also forms as a low temperature deposit in

fumaroles A fumarole (or fumerole) is a vent in the surface of the Earth or other rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcan ...

. It occurs associated with

pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue giv ...

, marcasite,

halotrichite Halotrichite, also known as ''feather alum'', is a highly hydrated sulfate of aluminium and iron. Its chemical formula is FeAl2(SO4)4·22H2O. It forms fibrous monoclinic crystals. The crystals are water-soluble. It is formed by the weathering and ...

pickeringite Pickeringite is a magnesium aluminium sulfate mineral with formula MgAl2(SO4)4·22(H2O). It forms a series with halotrichite. It forms as an alteration product of pyrite in aluminium rich rocks and in coal seams. It also occurs in pyrite rich hy ...

epsomite Epsomite, Epsom salt, or magnesium sulfate heptahydrate, is a hydrous magnesium sulfate mineral with formula MgSO4·7H2O. Epsomite crystallizes in the orthorhombic system as rarely found acicular or fibrous crystals, the normal form is as massiv ...

potash alum Potassium alum, potash alum, or potassium aluminium sulfate is a chemical compound: the double sulfate of potassium and aluminium, with chemical formula KAl(SO4)2. It is commonly encountered as the dodecahydrate, KAl(SO4)2·12H2O. It crystal ...

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 loss of water. It is a secondary sulfate mineral which forms from the oxidation of prim ...

and

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywa ...

. 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