Armbrusterite is a rare manganese-bearing silicate mineral found in alkaline igneous complexes. It typically presents as platy or tabular crystals and is notable for its distinct bright yellow fluorescence under short-wave ultraviolet light.
Is this armbrusterite?
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 armbrusterite with a known reference. Armbrusterite 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. Armbrusterite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Armbrusterite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: yellow, brown, greenish-brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: platy crystals, tabular aggregates.
Often confused with
Armbrusterite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside armbrusterite
Minerals reported to co-occur with armbrusterite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₅Na₆(Mn,Fe)₂Ti₂Si₁₆O₄₀(OH)₂·nH₂O
- Mohs hardness
- 3-4
- Density
- 2.68 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Platy Crystals, Tabular Aggregates
- Cleavage
- Perfect On {001}
- Fluorescence
- Bright Yellow Under SW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Alkaline Pegmatites
- Typical price
- $50-300 per specimen
Where rockhounds find armbrusterite
Classic worldwide localities
- Khibiny Massif, Russia
- Lovozero Massif, Russia
Field-hunting tip
Look in alkaline pegmatites country — that is the host setting where armbrusterite typically forms. If you start seeing aegirine, microcline, nepheline in float, you are in the right ground. Field specimens usually show a platy crystals, tabular aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find armbrusterite on the map
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