Size crystal mm.0,45 very nice. Collection and photo Edoardo Mazzola. From: Alpe Rosso, Orcesco, Druogno, Vigezzo Valley, Ossola Valley, Verbano-Cusio-Ossola Province, Piedmont, Italy — Photo: Edoardo Mazzola · CC0
Fersmite
Fersmite is an IMA-recognized mineral species in the halide class, with the chemical formula (Ca,Ce,Na)(Nb,Ta,Ti)₂(O,OH,F)₆.
It crystallizes in the orthorhombic crystal system (space group Pcan). It is a member of the Columbite structural group.
Key properties: Mohs hardness 4–4.5; specific gravity 4.69–4.8; Grayish brown streak; Resinous to subvitreous, submetallic luster; optically biaxial.
IMA symbol Fsm, grandfathered status — known before the IMA’s founding, named in 1946.
Found as a rare accessory mineral in nepheline syenites and carbonatites. In miarolitic cavities in an albitized pegmatite dike.
It is found associated with Columbite, pyrochlore, plagioclase, microcline, biotite, apatite, “hornblende”, titanite, muscovite, zircon, xenotime (Vishnevy Mountains, Russia); columbite.
The name refers to Academician Aleksandr Evgen’evich Fersman (1883–1945), eminent Russian mineralogist, geochemist, and gemologist.