Aldermanite is a very rare hydrated magnesium aluminum phosphate mineral typically found as small, fragile platy crystals or radial clusters. It is primarily known from phosphate-rich pegmatite deposits where it forms as a secondary mineral alongside other phosphate species.
Is this aldermanite?
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 aldermanite with a known reference. Aldermanite sits at Mohs ~2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: fibrous, flakes.
Often confused with
Aldermanite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Wavellite is the harder of the two (Mohs 3.5-4 vs. ~2); luster reads pearly on Aldermanite and vitreous to resinous, pearly on Wavellite.
How to tell apart: Montgomeryite is the harder of the two (Mohs 4 vs. ~2); luster reads pearly on Aldermanite and vitreous on Montgomeryite.
Often found alongside aldermanite
Minerals reported to co-occur with aldermanite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- [Mg(H₂O)₆][Na(H₂O)₂Al₃(PO₄)₂(OH)₆]·H₂O
- Mohs hardness
- ~2
- Density
- 2.0-2.15 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Fibrous, flakes
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- As a secondary mineral in cavities in a brecciated metamorphosed sedimentary phosphate deposit, formed by the alteration of fluellite (Moculta quarry, Australia)
Where rockhounds find aldermanite
Classic worldwide localities
- Moculta phosphate quarry, northeast of Angaston, South Australia
Field-hunting tip
Where it forms: As a secondary mineral in cavities in a brecciated metamorphosed sedimentary phosphate deposit, formed by the alteration of fluellite (Moculta quarry, Australia). If you start seeing fluellite in float, you are in the right ground. Typical habit: fibrous, flakes. Train your eye for that shape before scanning the outcrop.
Common questions
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Find aldermanite on the map
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