Tetraferriannite is a rare iron-rich mica member of the biotite group often found in alkaline igneous complexes. Collectors look for its dark, pseudohexagonal platy crystals that exhibit perfect basal cleavage typical of mica minerals. It is primarily identified through chemical analysis or occurrence in specific nepheline-syenite environments.
Is this tetraferriannite?
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 tetraferriannite with a known reference. Tetraferriannite 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. Tetraferriannite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Tetraferriannite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: black, dark brown, dark green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: platy, foliated, pseudohexagonal crystals.
Often confused with
Tetraferriannite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside tetraferriannite
Minerals reported to co-occur with tetraferriannite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KFe²⁺₃(Fe³⁺Si₃O₁₀)(OH)₂
- Mohs hardness
- 2.5-3
- Density
- 3.1-3.3 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Platy, Foliated, Pseudohexagonal Crystals
- Cleavage
- Perfect Basal
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Alkaline Igneous Rocks, Syenites, And Carbonatites
- Typical price
- $15-60 thumbnail
Where rockhounds find tetraferriannite
Classic worldwide localities
- Mont Saint-Hilaire, Quebec, Canada
- Khibiny Massif, Russia
- Magnet Cove, Arkansas, USA
- Norra Kärr, Sweden
Field-hunting tip
Look in alkaline igneous rocks, syenites, and carbonatites country — that is the host setting where tetraferriannite typically forms. If you start seeing nepheline, aegirine, microcline in float, you are in the right ground. Field specimens usually show a platy, foliated, pseudohexagonal crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify tetraferriannite?+
Where is tetraferriannite found?+
How much is tetraferriannite worth?+
What rocks look like tetraferriannite?+
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Find tetraferriannite on the map
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