Löllingite and siderite from Knappenberg, Hüttenberg, Carinthia, Austria — Photo: Kritzolina · CC BY-SA 4.0
Löllingite
Iron diarsenide — a silver-white mineral often intergrown with and hard to tell from arsenopyrite.
Intro adapted from Wikipedia (CC BY-SA).
Löllingite is an IMA-recognized mineral species in the sulfide class, with the chemical formula FeAs₂.
It crystallizes in the orthorhombic crystal system (space group Pnnm). It is a member of the Löllingite structural group.
Key properties: Mohs hardness 5–5.5; specific gravity 7.4; Grayish black streak; Metallic. Anisotropism: Strong. R1 –R2: (400) 51.6–59.7, (420) 52.0–59.9, (440) 52.6–59.8, (460) 53.1–58.8 luster.
IMA symbol Lö, grandfathered status — known before the IMA’s founding, named in 1845.
Found in mesothermal deposits in association with other sulfides and with calcite gangue; also in pegmatites.
It is found associated with Skutterudite, bismuth, nickeline, nickel-skutterudite, siderite, calcite.
The name refers to the Austrian locality at Lölling.