germanium

Stottite

Formula: Fe2+Ge(OH)6
Hydroxide, wickmanite group, germanium mineral
Specific gravity: 3.596 to 3.61
Hardness: 4½
Streak: Grey-white
Colour: Brown
Solubility:
Environments:

Hydrothermal environments

Stottite is very rare, with the highest concentration of germanium of any known mineral (AM 43.1006-1008).
The type locality is the Tsumeb Mine, Oshikoto Region, Namibia, and this is the only known locality to date (September 2019). Stottite is a secondary mineral formed in the oxidised zone of a germanium-rich dolostone-hosted hydrothermal polymetallic ore deposit (Webmin, HOM). It is formed in the deep oxidised orebody, at a depth of about 1000 metres, by the action of circulating water on renierite and germanite (Dana).
Stottite typically occurs in small cavities in partly oxidised massive sulphide ores that are enriched in germanium. The sulfide matrix of the type specimen comprises a mixture of renierite and germanite with bornite, tennantite and chalcocite.
In several other specimens stottite is associated with other secondary minerals including smithsonite, zinc-rich siderite, brunogeierite, schneiderhöhnite and ludlockite. renierite and, possibly, leiteite are also part of this paragenesis.
Leiteite, ludlockite, renierite, and schneiderhöhnite are all arsenites, in which arsenic occurs in its intermediate As(III) oxidation state. The occurrence of stottite in association with arsenites suggests that the paragenesis and, by implication, stottite itself, form under relatively reducing conditions (R&M 90.5.440-443).

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