Sepiolite is a unique clay mineral known for its low density, often floating on water in its natural state. Collectors identify it by its soft, chalky feel and its historic use in carving intricate tobacco pipes, a form commonly referred to as Meerschaum.
Is this sepiolite?
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 sepiolite with a known reference. Sepiolite 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: dull.
- 4Match the color rangeCompare against the expected color range: grayish white, yellowish white, bluish green white, reddish white, gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: earthy, fibrous.
Often confused with
Sepiolite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads dull on Sepiolite and pearly to dull earthy on Kaolinite.
How to tell apart: Magnesite is the harder of the two (Mohs 3.5-4.5 vs. 2-2.5); luster reads dull on Sepiolite and vitreous on Magnesite.
How to tell apart: Sepiolite is noticeably harder (Mohs 2-2.5 vs. 1); luster reads dull on Sepiolite and pearly, greasy, dull on Talc.
Often found alongside sepiolite
Minerals reported to co-occur with sepiolite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mg₄Si₆O₁₅(OH)₂·6H₂O
- Mohs hardness
- 2-2.5
- Density
- 2 g/cm³
- Colors
- Streak
- White
- Luster
- Dull
- Transparency
- Opaque or nearly so
- Crystal system
- Orthorhombic
- Crystal habit
- Earthy, fibrous
- Cleavage
- Perfect
- Rarity
- Common
- Uses
- Carving, Industrial, Collector, Decorative
- Host rock
- A sedimentary clay mineral; also in serpentine
Where rockhounds find sepiolite
1 mapped spotsClassic worldwide localities
- Middletown, Delaware Co., Pennsylvania, USA
- Gouverneur, St. Lawrence Co., New York, USA
- Little Cottonwood Canyon, Salt Lake Co., Utah, USA
- Crestmore, Riverside Co., California, USA
- Vallecas, near Madrid, and Cabañas, near Toledo, Spain
- Nugssuaq, western Greenland
Field-hunting tip
Where it forms: A sedimentary clay mineral; also in serpentine. If you start seeing opal, dolomite in float, you are in the right ground. Typical habit: earthy, fibrous. 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 sepiolite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
