Angastonite is a very rare hydrated calcium magnesium aluminum phosphate mineral. It typically occurs as small, delicate platy crystal aggregates within phosphate-rich zones in marble deposits.
Is this angastonite?
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 angastonite with a known reference. Angastonite 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: white.
- 5Look at form & habitCrystal system: triclinic. Typical habit: encrustations, platy.
Often confused with
Angastonite 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 Angastonite and vitreous to resinous, pearly on Wavellite.
How to tell apart: Variscite is the harder of the two (Mohs 4.5 vs. 2); luster reads pearly on Angastonite and vitreous to waxy on Variscite.
Often found alongside angastonite
Minerals reported to co-occur with angastonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaMgAl₂(PO₄)₂(OH)₄·7H₂O
- Mohs hardness
- 2
- Density
- 2.47 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly
- Transparency
- Transparent to translucent
- Crystal system
- Triclinic
- Crystal habit
- Encrustations, platy
- Cleavage
- One on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In phosphate mineralization in a gossanous weathered zone above recrystallized limestone (now marble)
Where rockhounds find angastonite
Classic worldwide localities
- Penrice marble quarry, ~2 km north of Angaston, South Australia (type locality)
Field-hunting tip
Where it forms: In phosphate mineralization in a gossanous weathered zone above recrystallized limestone (now marble). If you start seeing minyulite, perhamite, crandallite in float, you are in the right ground. Typical habit: encrustations, platy. Train your eye for that shape before scanning the outcrop.
Common questions
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Find angastonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
