Allophane is an amorphous, poorly ordered aluminosilicate mineral typically found as a secondary product in weathered volcanic soils or hydrothermal deposits. It is best identified by its clay-like, waxy appearance and tendency to occur in botryoidal or earthy masses, often requiring XRD analysis for positive confirmation.
Is this allophane?
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 allophane with a known reference. Allophane sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Allophane leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Allophane typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, blue, green, yellow, brown, colorless.
- 5Look at form & habitCrystal system: amorphous. Typical habit: earthy, massive, encrusting, botryoidal.
Often confused with
Allophane vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside allophane
Minerals reported to co-occur with allophane. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₂O₃·(SiO₂)₁₋₂·nH₂O
- Mohs hardness
- 3
- Density
- 1.8-2.0 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Amorphous
- Crystal habit
- Earthy, Massive, Encrusting, Botryoidal
- Cleavage
- None
- Rarity
- Common
- Uses
- Collector, Scientific Research
- Host rock
- Weathered Volcanic Ash, Hydrothermal Alteration Zones
- Typical price
- $10-50 for small samples
Where rockhounds find allophane
2 mapped spotsClassic worldwide localities
- Japan
- Germany
- New Zealand
- USA
- Russia
Field-hunting tip
Look in weathered volcanic ash, hydrothermal alteration zones country — that is the host setting where allophane typically forms. If you start seeing gibbsite, kaolinite, halloysite in float, you are in the right ground. Field specimens usually show a earthy, massive, encrusting, botryoidal habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Colorado, Missouri — start trip planning there.
Common questions
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Find allophane on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
