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, so Fencooperite leaves yellowish brown, Ekanite leaves white.
How to tell apart: Streak differs, so 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, 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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