Fencooperite is a rare iron-bearing silicate mineral typically found as tabular, hexagonal, brown crystals. It is most famously associated with the hyper-alkaline environments of the Khibiny Massif in Russia. Collectors prize it for its unique chemical structure and rarity within syenite pegmatites.
Is this fencooperite?
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 fencooperite with a known reference. Fencooperite 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. Fencooperite leaves a yellowish brown streak.
- 3Read the lusterHold the specimen under a strong light. Fencooperite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: dark brown, reddish brown.
- 5Look at form & habitCrystal system: trigonal. Typical habit: tabular hexagonal crystals, rosette-like aggregates.
Often confused with
Fencooperite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Ekanite is the harder of the two (Mohs 5-6 vs. 3-4); streak differs — Fencooperite leaves yellowish brown, Ekanite leaves white.
How to tell apart: Streak differs — Fencooperite leaves yellowish brown, Barytolamprophyllite leaves yellowish; luster reads vitreous on Fencooperite and pearly on Barytolamprophyllite.
Often found alongside fencooperite
Minerals reported to co-occur with fencooperite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ba₆Fe³⁺₃Si₈O₂₃(CO₃)₂Cl₃
- Mohs hardness
- 3-4
- Density
- 3.37 g/cm³
- Colors
- Streak
- Yellowish Brown
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Tabular Hexagonal Crystals, Rosette-like Aggregates
- Cleavage
- Perfect Basal
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Alkaline Pegmatites
- Typical price
- $50-300 per specimen
Where rockhounds find fencooperite
Classic worldwide localities
- Khibiny Massif, Russia
- Kola Peninsula, Russia
Field-hunting tip
Look in alkaline pegmatites country — that is the host setting where fencooperite typically forms. If you start seeing khibinskite, aegirine, nepheline in float, you are in the right ground. Field specimens usually show a tabular hexagonal crystals, rosette-like aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find fencooperite on the map
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