Brown crystals of the rare manganese mineral gonyerite from Harstigen mine (Pajsberg, Persberg, Filipstad, Värmland County, Sweden). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Gonyerite
Gonyerite is an IMA-recognized mineral species in the silicate class, with the chemical formula Mn²⁺₅Fe³⁺(Si₃Fe³⁺O₁₀)(OH)₈.
It crystallizes in the orthorhombic crystal system. It is a member of the Chlorite, Clay structural group.
Key properties: Mohs hardness 2.5; specific gravity 3.01; optically biaxial.
IMA symbol Gye, grandfathered status — known before the IMA’s founding, named in 1955.
Found in hydrothermal veinlets cutting skarn (Lº angban, Sweden).
It is found associated with Caryopilite, bementite, berzeliite, barite, garnet (Lº angban, Sweden).
In honor of Forest A. Gonyer, analytical chemist in the Department of Mineralogy and Petrography, Harvard University, Cambridge, Massachusetts, USA.