Stevensite is a rare, magnesium-rich member of the smectite clay group, typically forming as a secondary alteration product. It is characterized by its soft, soapy feel and dense, compact massive habit rather than visible crystals. Collectors often find it in evaporite deposits or as a replacement product in ultramafic rocks.
Is this stevensite?
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 stevensite with a known reference. Stevensite sits at Mohs 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 to resinous.
- 4Match the color rangeCompare against the expected color range: beige white, yellow brown, pink.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, radial.
Often confused with
Stevensite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads dull to resinous on Stevensite and greasy on Saponite.
How to tell apart: Stevensite is noticeably harder (Mohs 2.5 vs. 1); luster reads dull to resinous on Stevensite and pearly, greasy, dull on Talc.
Often found alongside stevensite
Minerals reported to co-occur with stevensite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Ca,Na)xMg₃-ySi₄O₁₀(OH)₂
- Mohs hardness
- 2.5
- Density
- 2.15-2.56 g/cm³
- Colors
- Streak
- White
- Luster
- Dull to resinous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, radial
- Cleavage
- Perfect on {001}
- Rarity
- Uncommon
- Uses
- Collector, Scientific research
- Host rock
- In cavities in basalt, formed by late-stage hydrothermal replacement of pectolite
Where rockhounds find stevensite
Classic worldwide localities
- Bergen Hill, Hudson Co., Springfield, Essex Co., Paterson, Passaic Co., New Jersey, USA
- Mine Creek, Bakersville, Mitchell Co., North Carolina, USA
- Prócida Island, Italy
- Corstorphine Hill, Edinburgh, Scotland
- Ohiri mine, Yamagata Prefecture, and the Akatani mine, Niigata Prefecture, Japan
Field-hunting tip
Where it forms: In cavities in basalt, formed by late-stage hydrothermal replacement of pectolite. If you start seeing quartz, talc, pectolite in float, you are in the right ground. Typical habit: fibrous, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify stevensite?+
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What rocks look like stevensite?+
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Find stevensite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
