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, 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.
