Endellite is the fully hydrated 10Å form of halloysite, often occurring as soft, clay-like masses or incrustations. It is notoriously unstable upon dehydration, meaning specimens should be stored in sealed containers to prevent them from turning into the 7Å variety.
Is this endellite?
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 endellite with a known reference. Endellite 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. Endellite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Endellite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: white, yellowish, gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive.
Often confused with
Endellite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside endellite
Minerals reported to co-occur with endellite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₂Si₂O₅(OH)₄·2H₂O
- Mohs hardness
- 2-2.5
- Density
- 2.0-2.2 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Massive
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Hydrothermal Alteration Zones in Igneous Rocks
- Typical price
- $10-60 per specimen
Where rockhounds find endellite
1 mapped spotsClassic worldwide localities
- Eureka, Utah, USA
- Lawrence County, Indiana, USA
- Angleur, Belgium
- Karlsbad, Czech Republic
Field-hunting tip
Look in hydrothermal alteration zones in igneous rocks country — that is the host setting where endellite typically forms. If you start seeing kaolinite, quartz, limonite in float, you are in the right ground. Field specimens usually show a massive habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah — start trip planning there.
Common questions
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Find endellite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
