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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to earthy, waxy.
- 4Match the color rangeCompare against the expected color range: white, green, blue, yellow, brown.
- 5Look at form & habitCrystal system: amorphous. Typical habit: botryoidal, encrustations, stalactitic.
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
- 2.75 g/cm³
- Streak
- White
- Luster
- Vitreous to earthy, waxy
- Transparency
- Translucent
- Crystal system
- Amorphous
- Crystal habit
- Botryoidal, encrustations, stalactitic
- Cleavage
- None
- Fluorescence
- Blue under SW UV
- Rarity
- Common
- Uses
- Collector, Scientific research
- Host rock
- A weathering product of volcanic ash
Where rockhounds find allophane
2 mapped spotsClassic worldwide localities
- Bisbee, and the Maid of Sunshine mine, Gleeson, Cochise Co., Arizona, USA
- Kelly, Socorro Co., New Mexico, USA
- Cerro Gordo, Inyo Co., California, USA
- Friedensville, Lehigh Co. and Cornwall, Lebanon Co., Pennsylvania, USA
- Gräfenthal, near Saalfeld, Thuringia, and at Schneeberg and Schwarzenberg, Saxony, Germany
- Jáchymov (Joachimsthal), Czech Republic
Field-hunting tip
Where it forms: A weathering product of volcanic ash. If you start seeing quartz, cristobalite, imogolite in float, you are in the right ground. Typical habit: botryoidal, encrustations, stalactitic. 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
How do you identify allophane?+
Where is allophane found?+
Can I find allophane in the United States?+
What rocks look like allophane?+
What minerals are found with allophane?+
What kind of rock does allophane form in?+
What is allophane used for?+
Find allophane on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
