Fettelite - group of tiny Fettelite xx on vug (0.6 mm across) from an unknown mine but somewhere in Chañarcillo district - FOV 2x2 mm — Photo: Maurizio Dini · CC BY 3.0
Fettelite
A mercury-silver-arsenic sulfosalt also known as sanguinite.
Intro adapted from Wikipedia (CC BY-SA).
Fettelite is an IMA-recognized mineral species in the sulfosalt class, with the chemical formula [Ag₆As₂S₇][Ag₁₀HgAs₂S₈].
It crystallizes in the monoclinic crystal system (space group C2). It is a member of the Fettelite structural group.
Key properties: Mohs hardness 3.75; specific gravity 6.29; Dark vermillion streak; Submetallic to metallic to adamantine luster.
IMA symbol Ftt, IMA status: approved, named in 1994.
A rare mineral found in low-temperature hydrothermal, silver-sulfosalt veins.
It is found associated with Proustite, pearceite, xanthoconite, safflorite.
The mineral was named to honor M. Fettel, a field geologist who first noted the mineral.