Mundrabillaite is a rare ammonium calcium phosphate mineral that typically forms as delicate, needle-like white crusts or efflorescences. It is primarily found in environments where bat guano reacts with calcium-rich substrates in caves or, famously, at the site of the Mundrabilla iron meteorite. Collectors prize it as a scientific curiosity due to its unusual association with phosphate-rich organic decay.
Is this mundrabillaite?
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 mundrabillaite with a known reference. Mundrabillaite 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. Mundrabillaite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Mundrabillaite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: crusts, aggregates of acicular crystals.
Often confused with
Mundrabillaite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside mundrabillaite
Minerals reported to co-occur with mundrabillaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (NH₄)₂Ca(HPO₄)₂·H₂O
- Mohs hardness
- 2
- Density
- 1.65 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Crusts, Aggregates of Acicular Crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Phosphate-rich Cave Deposits, Altered Meteorite Impact Sites
- Typical price
- niche/high, typically found only in research or advanced collections
Where rockhounds find mundrabillaite
Classic worldwide localities
- Mundrabilla meteorite site, Western Australia
- various cave environments
Field-hunting tip
Look in phosphate-rich cave deposits, altered meteorite impact sites country — that is the host setting where mundrabillaite typically forms. If you start seeing hannayite, newberyite, struvite in float, you are in the right ground. Field specimens usually show a crusts, aggregates of acicular crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find mundrabillaite on the map
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