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 5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: blue green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive.
Often confused with
Ferroalluaudite vs. its common look-alikes, and how to tell them apart in the field.
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
- 5
- Density
- 3.67 g/cm³
- Colors
- Streak
- Light yellow
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Massive
- Cleavage
- Good in one direction
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- From zoned granite pegmatites; in phosphatic nodules
Where rockhounds find ferroalluaudite
Classic worldwide localities
- Pleasant Valley pegmatite and the Helen Beryl mine, near Custer, Custer Co., South Dakota, USA
- Rapid Creek, Yukon Territory, Canada
- Angarf-Sud pegmatite, Tazenakht Plain, Anti-Atlas Mountains, Morocco
- Norrö pegmatite, on Rånö Island, Sweden
- Kiluli, Rwanda
Field-hunting tip
Where it forms: From zoned granite pegmatites; in phosphatic nodules. If you start seeing triphylite, barbosalite, ferrisicklerite in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferroalluaudite?+
Where is ferroalluaudite found?+
What rocks look like ferroalluaudite?+
What minerals are found with ferroalluaudite?+
What kind of rock does ferroalluaudite form in?+
What is ferroalluaudite used for?+
Find ferroalluaudite on the map
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