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Formula: ZnAl2(AsO4)(OH)5
Anhydrous arsenate containing hydroxyl
Crystal System: Triclinic
Specific gravity: 3.66 calculated
Streak: White
Colour: Yellowish brown to dark brown
Solubility: Insoluble in hydrochloric acid
Environments
gerdtremmelite is a very rare secondary mineral that to date (November
2021) has been reported only from the type locality.
Localities
At the type locality, the Tsumeb Mine, Tsumeb, Oshikoto Region, Namibia, gerdtremmelite occurs as a
secondary phase in deeply oxidised ore specimens in the
dolostone-hosted hydrothermal polymetallic ore deposit. It forms spherulitic
aggregates of tabular crystals up to 3 microns in size and approximately 1 micron in length. Associated minerals include
hematite, quartz,
scorodite, powellite,
betpakdalite, kaolinite,
wilhelmkleinite and adamite
(AM 71.845-847, HOM).
Gerdtremmelite from the Tsumeb Mine - Image
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