Colorless adamantine microcrystals of the extremely rare K-Al-Ta mineral sosedkoite in a partially polished specimen that was analyzed by the former owner of the specimen from the type and only known locality worldwide in Russia: Vasin-Myl'k Mountain, Voron'i Tundry, Murmansk Oblast, Russian Federation. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY 4.0
Sosedkoite
Sosedkoite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula K₅Al₂Ta₂₂O₆₀.
It crystallizes in the orthorhombic crystal system.
Key properties: specific gravity 6.9; Adamantine luster.
IMA symbol Sos, IMA status: approved, named in 1981.
Found in a granite pegmatite.
It is found associated with Microlite, simpsonite, cesstibtantite, stibiotantalite, alumotantite, natrotantite.
The mineral was named to honor Aleksandr Federovich Sosedko (1901–1957), Russian mineralogist, Institute of Geological Sciences, Academy of Sciences, Moscow, Russia.