Beidellite is a member of the smectite clay group known for its high swelling capacity when hydrated. It typically appears as massive, waxy, or earthy clay accumulations found in altered volcanic tuff or hydrothermal vein environments. Collectors usually identify it by its clay-like texture and its tendency to adhere to the tongue when dry.
Is this beidellite?
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 beidellite with a known reference. Beidellite sits at Mohs 1-2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Beidellite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Beidellite typically shows a dull luster.
- 4Match the color rangeCompare against the expected color range: white, yellow, gray, reddish.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive, earthy, clay-like.
Often confused with
Beidellite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside beidellite
Minerals reported to co-occur with beidellite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Na,Ca)₀.₅Al₄(Si,Al)₈O₂₀(OH)₄·nH₂O
- Mohs hardness
- 1-2
- Density
- 2.1-2.6 g/cm³
- Streak
- White
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Massive, Earthy, Clay-like
- Cleavage
- Perfect
- Rarity
- Common
- Uses
- Industrial, Scientific, Collector
- Host rock
- Hydrothermal Alteration Zones, Sedimentary Clays, Volcanic Ash Deposits
- Typical price
- $10-30 for reference specimens
Where rockhounds find beidellite
1 mapped spotsClassic worldwide localities
- Beidell, Colorado, USA
- France
- Japan
- Germany
Field-hunting tip
Look in hydrothermal alteration zones, sedimentary clays, volcanic ash deposits country — that is the host setting where beidellite typically forms. If you start seeing quartz, calcite, zeolites in float, you are in the right ground. Field specimens usually show a massive, earthy, clay-like 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
How do you identify beidellite?+
Where is beidellite found?+
Can I find beidellite in the United States?+
How much is beidellite worth?+
What rocks look like beidellite?+
What minerals are found with beidellite?+
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Find beidellite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
