Alluaudite is a phosphate mineral commonly found as an alteration product of triphylite in complex pegmatites. It typically occurs as yellowish to brownish granular or fibrous masses rather than well-defined crystals, making it a challenging but rewarding find for phosphate mineral enthusiasts.

Hardness

5-5.5

Mohs

Luster

Vitreous to resinous

Streak

Dirty yellow

Transparency

Subtranslucent to opaque

mineraluncommon

Alluaudite

Hardness: 5-5.5
Luster: Vitreous to resinous
Streak: Dirty yellow
Transparency: Subtranslucent to opaque

Is this alluaudite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch alluaudite with a known reference. Alluaudite sits at Mohs 5-5.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: dirty yellow.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous to resinous.
4
Match the color range
Compare against the expected color range: yellow, brownish yellow, green, black.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: fibrous, nodular, platy.

Often confused with

Alluaudite vs. its common look-alikes, and how to tell them apart in the field.

mineral

Triphylite

Mohs 4-5

How to tell apart: Streak differs, so Alluaudite leaves dirty yellow, Triphylite leaves white to grayish white.

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Often found alongside alluaudite

Minerals reported to co-occur with alluaudite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: □NaMnFe₂(PO₄)₃
Mohs hardness: 5-5.5
Density: 3.45 g/cm³
Colors: Yellow Brownish yellow Green Black
Streak: Dirty yellow
Luster: Vitreous to resinous
Transparency: Subtranslucent to opaque
Crystal system: Monoclinic
Crystal habit: Fibrous, nodular, platy
Cleavage: {010}, {110}, and {11̄0}, good
Rarity: Uncommon
Uses: Collector, Scientific research
Host rock: Very common in granite pegmatites, formed by sodium metasomatism of triphylite-lithiophilite, heterosite-purpurite, or ferrisicklerite; in phosphatic nodules in shales

Where rockhounds find alluaudite

Classic worldwide localities

G.E. Smith mine, near Newport, Sullivan Co., New Hampshire, USA
La Vilate quarry, near Chanteloube, Haute-Vienne, France
Dolní Bory, near Velkého Meziřičí, Czech Republic
Varuträsk pegmatite, Västerbotten, Sweden
Tremearne pegmatite, Breage, Cornwall, England
Rapid Creek, Yukon Territory, Canada

Field-hunting tip

Where it forms: Very common in granite pegmatites, formed by sodium metasomatism of triphylite-lithiophilite, heterosite-purpurite, or ferrisicklerite; in phosphatic nodules in shales. If you start seeing triphylite, arrojadite, satterlyite in float, you are in the right ground. Typical habit: fibrous, nodular, platy. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify alluaudite?+

Mohs hardness is 5-5.5. Luster: vitreous to resinous. The streak is dirty yellow. Common colors include yellow, brownish yellow, green, black.

Where is alluaudite found?+

Notable localities include G.E. Smith mine, near Newport, Sullivan Co., New Hampshire, USA; La Vilate quarry, near Chanteloube, Haute-Vienne, France; Dolní Bory, near Velkého Meziřičí, Czech Republic; Varuträsk pegmatite, Västerbotten, Sweden; Tremearne pegmatite, Breage, Cornwall, England.

What rocks look like alluaudite?+

Alluaudite is most often confused with Triphylite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with alluaudite?+

Alluaudite commonly co-occurs with Triphylite, Arrojadite, Satterlyite, Wicksite, Wolfeite, Pyrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does alluaudite form in?+

Where it forms: Very common in granite pegmatites, formed by sodium metasomatism of triphylite-lithiophilite, heterosite-purpurite, or ferrisicklerite; in phosphatic nodules in shales. Working float back to the host body is the standard way to chase a fresh occurrence.

What is alluaudite used for?+

Alluaudite is used in collector, scientific research.

Find alluaudite on the map

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