Niobophyllite is a rare member of the astrophyllite group, distinguished primarily by its high niobium content. It forms distinct golden-bronze bladed or star-shaped aggregates, often found embedded in alkaline igneous rocks. Collectors prize it for its unique habit and similarity to the more common astrophyllite.
Is this niobophyllite?
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 niobophyllite with a known reference. Niobophyllite sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellowish-brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to adamantine.
- 4Match the color rangeCompare against the expected color range: brown.
- 5Look at form & habitCrystal system: triclinic. Typical habit: flakes, foliated.
Often confused with
Niobophyllite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Niobophyllite leaves yellowish-brown, Astrophyllite leaves golden; luster reads vitreous to adamantine on Niobophyllite and submetallic, pearly, greasy on Astrophyllite.
How to tell apart: Streak differs, so Niobophyllite leaves yellowish-brown, Kupletskite leaves brown.
Often found alongside niobophyllite
Minerals reported to co-occur with niobophyllite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₂NaFe₇(Nb,Ti)₂(Si₄O₁₂)₂O₂(OH)₄(O,F)
- Mohs hardness
- 3-4
- Density
- 3.42 g/cm³
- Colors
- Streak
- Yellowish-brown
- Luster
- Vitreous to adamantine
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Flakes, foliated
- Cleavage
- Perfect on {001}, poor on f0klg
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- As discontinuous seams and polycrystalline aggregates within a paragneiss intruded by an alkalic syenite (Seal Lake, Canada)
Where rockhounds find niobophyllite
Classic worldwide localities
- Seal Lake, Labrador, Newfoundland, Canada
Field-hunting tip
Where it forms: As discontinuous seams and polycrystalline aggregates within a paragneiss intruded by an alkalic syenite (Seal Lake, Canada). If you start seeing albite, arfvedsonite, aegirine-augite in float, you are in the right ground. Typical habit: flakes, foliated. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify niobophyllite?+
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What rocks look like niobophyllite?+
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Find niobophyllite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
