Ferroalluaudite is a relatively rare phosphate mineral typically occurring as a secondary alteration product in phosphate-rich granite pegmatites. It is best identified by its distinct yellowish-brown to greenish hues and its association with other phosphate minerals in hydrothermal veins or weathered zones.
Is this ferroalluaudite?
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 ferroalluaudite with a known reference. Ferroalluaudite sits at Mohs 4-5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Ferroalluaudite leaves a light yellow streak.
- 3Read the lusterHold the specimen under a strong light. Ferroalluaudite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, brown, green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, massive, or granular.
Often confused with
Ferroalluaudite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Ferroalluaudite leaves light yellow, Alluaudite leaves yellowish white; luster reads vitreous on Ferroalluaudite and vitreous to resinous on Alluaudite.
How to tell apart: Streak differs — Ferroalluaudite leaves light yellow, Hagendorfite leaves light green.
Often found alongside ferroalluaudite
Minerals reported to co-occur with ferroalluaudite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na(Fe³⁺,Fe²⁺)₂(PO₄)₂
- Mohs hardness
- 4-5
- Density
- 3.35-3.50 g/cm³
- Streak
- Light Yellow
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, Massive, Or Granular
- Cleavage
- Good in One Direction
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Granite Pegmatites
- Typical price
- $20-150 for micromounts or small cabinet specimens
Where rockhounds find ferroalluaudite
Classic worldwide localities
- Buranga, Rwanda
- Pegmatite de Hagendorf, Germany
- Sapucaia Mine, Brazil
Field-hunting tip
Look in granite pegmatites country — that is the host setting where ferroalluaudite typically forms. If you start seeing triphylite, lithiophilite, variscite in float, you are in the right ground. Field specimens usually show a fibrous, massive, or granular habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find ferroalluaudite on the map
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