Grey crystals of this very rare bismuth selenide from one of the most famous localities from the species: Falun Mine, Falun, Dalarna, Sweden. — Photo: David Hospital · CC BY-SA 4.0
Laitakarite
Laitakarite is an IMA-recognized mineral species in the sulfide class, with the chemical formula Bi₄(Se,S)₃.
It crystallizes in the hexagonal crystal system (space group R-3m). It is a member of the Tetradymite structural group.
Key properties: specific gravity 8.12; Metallic. Anisotropism: Moderate, pale brown to dark gray. R1 –R2: (400) 50.6–53.8, (420) 50.4–54.0, (440) 50.2–54.2 luster.
IMA symbol Ltk, IMA status: approved, named in 1959.
Found in veinlets in quartz-anthophyllite-cordierite-biotite rocks (Orijärvi mine, Finland).
It is found associated with Chalcopyrite, bismuth, sphalerite, molybdenite, silver, pyrite, galena (Orijärvi mine, Finland); tetrahedrite–tennantite, luzonite–famatinite, pyrite.
The name refers to Professor Aarne Laitakari (1890–1975), Director, Geological Survey of Finland, who collected the original material.