Johannite - Encyclopedia

    Class : Sulfates, chromates, molybdates
    Subclass : Hydrated sulfates
    Crystal system : Triclinic
    Chemistry : Cu(UO2)2(SO4)2(OH)2 8H2O
    Rarity : Uncommon


Johannite is a sulfate of copper and uranium. It is a secondary mineral from the oxidation zone of copper-rich uranium deposits. Its genesis seems to derive from the oxidation of uraninite in the presence of gypsum. Its name was given to it in honor of Archduke Johann Baptiste Joseph Fabian Sebastian of Austria, founder of the Styrian Landesmuseum in Graz. Johannite forms thick tabular to prismatic crystals, spheroidal aggregates and coatings in greenish-yellow to dark emerald green color.

Main photo : Johannite from Paitzdorf, Greiz District, Germany © Stephan Wolfsried

Johannite from Krunkelbach Valley Uranium deposit, Germany © Carsten Slotta
Johannite from Jáchymov, Czech Republic © Elmar Lackner
Johannite from Markey Mine, Utah, USA © Alex Earl
Johannite from Markey Mine, Utah, USA © Alex Earl

Johannite in the World

Johannite is known in crystals in the uranium veins of Jachymov (Czech Republic) and Johanngeorgenstadt (Germany). It is also known in the Gabonese mine of Mounana and in several uranium deposits in Colorado and Utah.

Johannite in France

In France, joahnnite is present in the pitchblende vein of the Limouzat mine in Bois Noirs (Loire), at Mas d'Alary (Hérault), at Davignac near Ussel (Corrèze) and at Quistiav (Morbihan).

Twinning

Twins are known around the [001] axis, and with {010} as the composition plane.

Fakes and treatments

No fakes recorded for this mineral species.



Hardness : 2 to 2.5
Density : 3.32
Fracture : Undetermined
Streak : Pale green


TP : Translucent to transparent
RI : 1.572 to 1.616
Birefringence : 0.040
Optical character : Biaxial (+/-)
Pleochroism : Strong
Fluorescence : None


Solubility : Acids, water

Magnetism : NoneRadioactivity : Strong

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