Hydrated sulphate containing hydroxyl
Specific gravity: 3.32
Hardness: 2 to 2½
Streak: Pale green
Colour: Emerald-green, apple-green
Solubility: Decomposed by water, soluble in acids
Johannite is a rare secondary mineral in the oxidised
portions of sulphide-bearing uraninite deposits, commonly of post-mine
formation. Associated minerals include gypsum,
brochantite and chalcanthite
The type locality is the Elias mine, Jáchymov, Karlovy Vary District, Karlovy Vary Region, Czech Republic.
At La Creusa Uranium prospect, La Creusaz, Les Marécottes, Salvan, Saint-Maurice, Valais, Switzerland, johannite is associated with marécottite (MinRec 35.4.358).
Back to Minerals