Terminated crystal of niocalite in carbonatite matrix. Total length of crystal was 5mm. Collected 2007 - Donald Doell. From: St Lawrence Columbium Mine, Oka complex, Oka, Deux-Montagnes RCM, Laurentides, Québec, Canada. — Photo: Donald Doell · CC0
Niocalite
Niocalite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ca₇Nb(Si₂O₇)₂O₃F.
It crystallizes in the monoclinic crystal system (space group Pa). It is a member of the Wöhlerite structural group.
Key properties: Mohs hardness 6; specific gravity 3.32; Vitreous luster; optically biaxial.
IMA symbol Nio, grandfathered status — known before the IMA’s founding, named in 1956.
Found in coarse-grained strontian carbonatite.
It is found associated with Calcite, magnetite, apatite, diopside, biotite, pyrochlore, niobian perovskite.
The name refers to NIObium and CALcium in the composition.