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Formula: [Ag6As2S7][Ag10FeAs2S8]
Sulphosalt, silver- and arsenic- bearing
mineral
Crystal System: Monoclinic
Specific gravity: 5.74 calculated
Streak: Dark reddish grey
Environments
Plutonic igneous environments
Hydrothermal environments
Ferrofettelite is a new mineral, approved in 2021 and to date (June 2022) reported only from the type locality.
Localities
At the type locality, Glasberg quarry, Nieder-Beerbach, Mühltal, Darmstadt-Dieburg, Darmstadt, Hesse, Germany,
ferrofettelite occurs as anhedral to subhedral flakes and grains up to 80 μm, associated with
proustite and xanthoconite, on
arsenolite, calcite and
prehnite
(MM 86.2.340-345).
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