Franconite is a rare niobium-bearing mineral typically found as white, platy, or fan-shaped crystalline aggregates. It is almost exclusively known to collectors from the alkaline intrusive complexes in Quebec, particularly the Francon and Poudrette quarries where it occurs in vugs within igneous rocks.
Is this franconite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch franconite with a known reference. Franconite sits at Mohs 4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to adamantine, silky on fractures.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: aggregates, bladed.
Often confused with
Franconite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Franconite is noticeably harder (Mohs 4 vs. 2); streak differs, so Franconite leaves white, Ikunolite leaves dark gray; luster reads vitreous to adamantine, silky on fractures on Franconite and metallic on Ikunolite.
How to tell apart: Gonnardite is the harder of the two (Mohs 5 vs. 4); luster reads vitreous to adamantine, silky on fractures on Franconite and silky on Gonnardite.
Often found alongside franconite
Minerals reported to co-occur with franconite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaNb₂O₅(OH)·3H₂O
- Mohs hardness
- 4
- Density
- 2.72 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous to adamantine, silky on fractures
- Transparency
- Transparent to opaque
- Crystal system
- Monoclinic
- Crystal habit
- Aggregates, bladed
- Cleavage
- Basal, parting
- Fluorescence
- Yellow white under SW and LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In vugs of a dawsonite-bearing sill in a limestone deposit (Francon quarry, Canada)
Where rockhounds find franconite
Classic worldwide localities
- Francon quarry, Montreal Island, Montreal, at Mont Saint-Hilaire, and near Saint-Amable, Quebec, Canada
- Vishnevogorsk alkalic complex, Vishnevy-Ilmen Mountains, Southern Ural Mountains, Russia
Field-hunting tip
Where it forms: In vugs of a dawsonite-bearing sill in a limestone deposit (Francon quarry, Canada). If you start seeing hochelagaite, weloganite, calcite in float, you are in the right ground. Typical habit: aggregates, bladed. Train your eye for that shape before scanning the outcrop.
Common questions
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Find franconite on the map
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