Sillénite
A rare bismuth-silicon oxide named for Swedish chemist Lars Gunnar Sillén, found with bismutite.
Intro adapted from Wikipedia (CC BY-SA).
Sillénite is an IMA-recognized mineral species in the silicate class, with the chemical formula Bi₁₂SiO₂₀.
It crystallizes in the cubic crystal system (space group I23).
Key properties: specific gravity 9.16; Light yellowish to brownish white streak; Adamantine luster.
IMA symbol Sén, grandfathered status — known before the IMA’s founding, named in 1943.
Forms secondarily through oxidation of bismuth-bearing minerals (Durango, Mexico); in a hydrothermal vein in skarns (Fuka, Japan).
It is found associated with Bismutite (Durango, Mexico); shattuckite, a joite, duhamelite (Munihuaza, Mexico); calcite (Fuka, Japan).
In honor of Dr. Lars Gunnar Sill¶en (1916{), Swedish chemist of Stockholm, Sweden.