White aggregates of franconite on a single sharp weloganite crystal, from the type locality Francon (Francon Quarry, Québec, Canada). Franconite is a niobium mineral found in a very few localities worldwide. — Photo: David Hospital · CC BY-SA 4.0
Franconite
Franconite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula NaNb₂O₅(OH)·3H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/c).
Key properties: specific gravity 2.72; White streak; Vitreous to adamantine, silky on fractures luster; optically biaxial.
IMA symbol Fra, IMA status: approved, named in 1981.
Found in vugs of a dawsonite-bearing sill in a limestone deposit (Francon quarry, Canada); in cavities in altered pegmatite dikes, hornfels, sodalite syenite, or miarolitic cavities.
It is found associated with Hochelagaite, weloganite, calcite, quartz (Francon quarry, Canada); burbankite, muscovite, albite, microcline, chlorite, calcite, strontianite.
The name refers to the Francon quarry, Montreal, Canada, where it was first found.