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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
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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