Fiemmeite crystals — Photo: Francesco Demartin, Italo Campostrini, Paolo Ferretti Ivano Rocchetti · CC BY 4.0
Fiemmeite
Fiemmeite is an IMA-recognized mineral species in the organic mineral class, with the chemical formula Cu₂(C₂O₄)(OH)₂·2H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/c). It is a member of the Not in a structural group, Oxalate structural group.
Key properties: specific gravity 2.78; Pale blue streak; Vitreous to waxy luster.
IMA symbol Fmm, IMA status: approved, named in 2018.
Found in coalified wood trunks in continental sandstone which were permeated by mineralizing solutions containing Cu, U, As, Pb and Zn. The mineralization is a “sandstone-uranium type” roll front deposit.
It is found associated with Baryte, olivenite, middlebackite, moolooite, brochantite, cuprite, devilline, malachite, azurite, zeunerite/metazeunerite, tennantite, chalcocite, galena.
The name is derived from the locality near where the first specimens were collected.