Alunogen - Encyclopedia
Class : Sulphates, chromates, molybdates
Subclass : Hydrated sulphates
Crystal System : Triclinic
Chemistry : Al2(SO4)3 17H2O
Rarity : Uncommon
Alunogen is an hydrated aluminum sulphate, it is above all a mineral of arid regions where its formation results from the reaction of sulfuric acid formed by oxidation of pyrite on aluminous rocks. It forms efflorescences, fibrous encrustations or rare and small prismatic crystals of pseudohexagonal appearance, in the oxidation zones of sulphide deposits. This mineral has been known since Antiquity, its name comes from the Latin alumen (alun) and the Greek genos (origin), in reference to its use as a source of alum. It is also found in coal mines, where it is formed by the same process by the destruction of pyrite, as well as in fumaroles and solfataras. It is a theoretically colorless mineral, but usually tinted yellow or red by impurities.
Alunogen in the World
Twinning
This species twins with {010}, but they are not visible to the naked eye.
Fakes and treatments
Hardness : 1.5 to 2
Density : Not measured
Fracture : Fibrous
Trace : White
TP : Translucent to transparent
RI : 1.473 to 1.480
Birefringence : 0.007
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None
Solubility : Water
Magnetism : None
Radioactivity : None