Halloysite is a clay mineral frequently found as an alteration product of aluminosilicate minerals. It is best identified by its distinct tubular micro-structure and earthy texture, which sets it apart from other kaolinite-group minerals in fine detail.
Is this halloysite?
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 halloysite with a known reference. Halloysite sits at Mohs 2-2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Halloysite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Halloysite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: white, off-white, gray, yellowish.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tubular, clay-like, earthy, massive.
Often confused with
Halloysite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside halloysite
Minerals reported to co-occur with halloysite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₂Si₂O₅(OH)₄
- Mohs hardness
- 2-2.5
- Density
- 2.0-2.6 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Tubular, Clay-like, Earthy, Massive
- Cleavage
- None
- Rarity
- Common
- Uses
- Ceramics, Industrial Absorbent, Catalyst Carrier
- Host rock
- Weathered Volcanic Ash Deposits, Hydrothermal Clay Veins
- Typical price
- $5-30 for small samples
Where rockhounds find halloysite
5 mapped spotsClassic worldwide localities
- USA
- New Zealand
- China
- France
- Japan
Field-hunting tip
Look in weathered volcanic ash deposits, hydrothermal clay veins country — that is the host setting where halloysite typically forms. If you start seeing kaolinite, quartz, illite in float, you are in the right ground. Field specimens usually show a tubular, clay-like, earthy, massive habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Georgia, Colorado, North Carolina — start trip planning there.
Common questions
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Find halloysite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
