Ferrotochilinite
Ferrotochilinite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula FeS·≈0.85[Fe(OH)₂].
It crystallizes in the monoclinic crystal system (space group C2/m). It is a member of the Tochilinite structural group.
Key properties: Mohs hardness 1; specific gravity 3.467; Black streak; Metallic (fresh), dull, or tarnishes to iridescent purplish or golden-brown luster.
IMA symbol Ftch, IMA status: approved, named in 2010.
Of low-temperature hydrothermal origin coating cavities in pentlandite-mooihoekite- cubanite ore with minor magnetite and chalcopyrite.
It is found associated with Ferrovalleriite, magnetite, an Fe-rich chlorite-type phyllosilicate.
As the structural analogue (based on chemical, X-ray, and IR data similarities) of tochilinite with essential ferrous iron.