Macroscopic image of the rock sample containing ferrofettelite (dark red). Scale bar and sample number are indicated. The image is published in an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( https://creativecommons.org/licenses/by/4.0/ ). — Photo: Luca Bindi and Robert T. Downs · CC BY-SA 4.0
Ferrofettelite
Ferrofettelite is an IMA-recognized mineral species in the sulfosalt class, with the chemical formula [Ag₆As₂S₇][Ag₁₀FeAs₂S₈].
It crystallizes in the monoclinic crystal system (space group C2). It is a member of the Fettelite structural group.
Key properties: Mohs hardness 3.5; specific gravity 5.74; Dark reddish gray streak; Metallic luster.
IMA symbol Fftt, IMA status: approved, named in 2021.
It is found associated with Proustite, xanthoconite, arsenolite, calcite, prehnite.
The prefix indicates the Fe-analogue of fettelite.