Fluorannite is a rare mica mineral characterized by a high fluorine content within its octahedral and interlayer structure. It typically appears as brown to greenish-brown tabular crystals within alkaline igneous environments, often closely resembling other members of the biotite series.
Is this fluorannite?
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 fluorannite with a known reference. Fluorannite sits at Mohs 2.5-3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Fluorannite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Fluorannite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: brown, greenish-brown, yellowish-brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, micaceous masses.
Often confused with
Fluorannite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Luster reads vitreous on Fluorannite and pearly on Biotite.
How to tell apart: Luster reads vitreous on Fluorannite and pearly on Phlogopite.
How to tell apart: Luster reads vitreous on Fluorannite and pearly on Annite.
Often found alongside fluorannite
Minerals reported to co-occur with fluorannite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KFe₃²⁺(AlSi₃O₁₀)F₂
- Mohs hardness
- 2.5-3
- Density
- 3.0-3.2 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular Crystals, Micaceous Masses
- Cleavage
- Perfect Basal
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Alkaline Igneous Rocks
- Typical price
- $20-100 per specimen
Where rockhounds find fluorannite
Classic worldwide localities
- Khibiny Massif, Russia
- Ilmen Mountains, Russia
- Mont Saint-Hilaire, Canada
- Magnet Cove, USA
Field-hunting tip
Look in alkaline igneous rocks country — that is the host setting where fluorannite typically forms. If you start seeing nepheline, aegirine, microcline in float, you are in the right ground. Field specimens usually show a tabular crystals, micaceous masses habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find fluorannite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
