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Formula: NaCuMg3(AsO4)3
Anhydrous normal arsenate,
alluaudite group.
Johillerite forms a continuous solid-solution system with badalovite and
nickenichite, and a discontinuous solid solution with
bradaczekite
(CM 56 189–201).
Crystal System: Monoclinic
Specific gravity: 4.15 measured, 4.21 calculated
Hardness: 3
Streak: White
Colour: Violet
Environments
Hydrothermal environments
Fumeroles
Localities
At the type locality, the Tsumeb Mine, Tsumeb, Oshikoto Region, Namibia, johillerite has been recognised in the oxidised
zone of the polymetallic sulphide deposit, only in a single specimen consisting of altered
tennantite with chalcocite. In cavities
in this specimen the succession of secondary minerals is
conichalcite to copper-bearing
adamite to johillerite
(AM 67.1075).
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