Bettertonite is a rare aluminum arsenate, typically white. It was approved as a distinct mineral species in 2014. It was first described from the Penberthy Croft mine, St. Hilary, Cornwall, England.
Is this bettertonite?
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 bettertonite with a known reference. Bettertonite 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: vitreous to pearly, somewhat silky.
- 4Match the color rangeCompare against the expected color range: white, rarely pale orange.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: platy crystals.
Often confused with
Bettertonite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads vitreous to pearly, somewhat silky on Bettertonite and satiny to greasy or waxy on Hydrotalcite.
How to tell apart: Luster reads vitreous to pearly, somewhat silky on Bettertonite and pearly on Meixnerite.
Often found alongside bettertonite
Minerals reported to co-occur with bettertonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₆(AsO₄)₃(OH)₉(H₂O)₅·11H₂O
- Mohs hardness
- 2
- Density
- 2.02 g/cm³
- Colors
- WhiteRarely pale orange
- Streak
- White
- Luster
- Vitreous to pearly, somewhat silky
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Platy crystals
- Cleavage
- Perfect on (010)
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Extremely rare, in quartz veins in a multi-stage, polymetallic hydrothermal deposit; probably formed from leaching and the replacement of Al to Fe in pharmacosiderite
Where rockhounds find bettertonite
Classic worldwide localities
- Penberthy Croft mine, ~1.5 km from the village of Goldsithney, St. Hilary, Cornwall, England
Field-hunting tip
Where it forms: Extremely rare, in quartz veins in a multi-stage, polymetallic hydrothermal deposit; probably formed from leaching and the replacement of Al to Fe in pharmacosiderite. If you start seeing arsenopyrite, chamosite, liskeardite in float, you are in the right ground. Typical habit: platy crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify bettertonite?+
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Find bettertonite on the map
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