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, 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.
