Mansfieldite is an uncommon hydrated aluminum arsenate mineral often occurring as a secondary mineral in oxidized ore zones. It is typically found as small, crusty, or radial aggregates and is structurally related to variscite. Because it contains arsenic, it should be handled with care by collectors.
Is this mansfieldite?
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 mansfieldite with a known reference. Mansfieldite sits at Mohs 3.5, 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.
- 4Match the color rangeCompare against the expected color range: white, light gray, reddish gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: encrustations, spherical.
Often confused with
Mansfieldite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside mansfieldite
Minerals reported to co-occur with mansfieldite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- AlAsO₄·2H₂O
- Mohs hardness
- 3.5
- Density
- 3.03 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Orthorhombic
- Crystal habit
- Encrustations, spherical
- Cleavage
- Indistinct on {201}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A hydrothermal product in altered and mineralized andesitic pyroclastic rocks (Hobart Butte, Oregon, USA)
Where rockhounds find mansfieldite
Classic worldwide localities
- Hobart Butte, about 22 km south of Cottage Grove, Lane Co., Oregon, USA
- Found in the Sara Alicia mine, near Alamos, Sonora, Mexico
- Neubulach, Black Forest, and Puderbach, Westerwald, Germany
- Cap Garonne mine, near le Pradet, Var, France
- Penberthy Croft mine, St. Hilary, Cornwall, England
- Djebel Debar, northeast of Hammam Meskhoutine, Qacentina (Constantine), Algeria
Field-hunting tip
Where it forms: A hydrothermal product in altered and mineralized andesitic pyroclastic rocks (Hobart Butte, Oregon, USA). If you start seeing kaolinite, quartz, scorodite in float, you are in the right ground. Typical habit: encrustations, spherical. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify mansfieldite?+
Where is mansfieldite found?+
Is mansfieldite safe to handle?+
What rocks look like mansfieldite?+
What minerals are found with mansfieldite?+
What kind of rock does mansfieldite form in?+
What is mansfieldite used for?+
Find mansfieldite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
