Alunogen
Alunogen, also called feather alum and hair salt is a colourless to white fibrous to needle-like aluminium sulfate mineral. It has the chemical formula Al23·17H2O.
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. 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: 23.5H2O. The second formula shows that H2O in the alunogen formula occurs both as ligand and loosely bound form.
