Images
Formula: NaNb2O5(OH).3H2O
Hydroxide, franconite group,
niobium-bearing mineral
Crystal System: Monoclinic
Specific gravity: 2.72 measured, 2.71 calculated
Hardness: 4
Streak: White
Colour: White, colourless, greyish blue
Luminescence: Franconite from the Poudrette Quarry fluoresces pale yellow under long wave UV, more intensely
under short wave
Environments
Plutonic igneous environments
Pegmatites
Localities
At the Poudrette quarry, Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada,
franconite occurs in cavities in altered pegmatite
dikes, hornfels, sodalite
syenite, or miarolitic cavities, associated with an intrusive alkalic
gabbro-syenite complex
(HOM).
Franconite from the Poudrette Quarry -
Image
At the type locality, the Francon quarry, Montréal, Québec, Canada, franconite occurs as white globules in
vugs in a dawsonite-bearing sill in the upper levels of the
limestone quarry. It is present most frequently on
weloganite crystals, and less commonly on crystals of
quartz and calcite;
hochelagaite is another associated mineral. The diameter of
franconite globules averages about 150 microns, but clustering is common, and groups up to 0.5 mm in diameter
have been found. Franconite has a vitreous lustre, but each globule consists of radiating, bladed crystals
that collectively impart a silky lustre to new surfaces of split globules. Franconite from this locality is
not fluorescent under UV, unlike that from the Poudrette quarry
(CM 22.2.239-243, HOM).
Franconite from the Francon Quarry -
Image
At the Vishnevye Mountains, Chelyabinsk Oblast, Russia, franconite is associated with
burbankite, muscovite,
albite, microcline,
chlorite, calcite,
strontianite and natrolite
(HOM).
Back to Minerals