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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly, waxy, or dull.
- 4Match the color rangeCompare against the expected color range: white, yellowish white, reddish white, brownish white, greenish white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: earthy.
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
- 2.55-2.565 g/cm³
- Streak
- White
- Luster
- Pearly, waxy, or dull
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Earthy
- Cleavage
- {001}, probable
- Rarity
- Common
- Uses
- Ceramics, Industrial absorbent, Catalyst carrier
- Host rock
- A product of hydrothermal alteration or surface weathering of aluminosilicate minerals, as feldspars
Where rockhounds find halloysite
5 mapped spotsClassic worldwide localities
- Wagon Wheel Gap, Mineral Co., Colorado, USA
- Gonzales, Gonzales Co., Texas, USA
- Bedford, Lawrence Co., Indiana, USA
- Horse Cove, Hart Co., Kentucky, USA
- Bergnersreuth, near Wunsiedel, Bavaria, Germany
Field-hunting tip
Where it forms: A product of hydrothermal alteration or surface weathering of aluminosilicate minerals, as feldspars. If you start seeing kaolinite, endellite, allophane in float, you are in the right ground. Typical habit: earthy. 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
How do you identify halloysite?+
Where is halloysite found?+
Can I find halloysite in the United States?+
What rocks look like halloysite?+
What minerals are found with halloysite?+
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Find halloysite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
