Sassolite is a rare, water-soluble mineral that typically forms as white, scaly crusts or tabular crystals around volcanic fumaroles. It is best identified by its pearly luster and soft, soapy feel, though collectors must store it in dry environments to prevent dissolution due to its extreme solubility in water.
Is this sassolite?
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 sassolite with a known reference. Sassolite sits at Mohs 1, 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: pearly.
- 4Match the color rangeCompare against the expected color range: white, gray, yellow, brown.
- 5Look at form & habitCrystal system: triclinic. Typical habit: encrustations, platy, tabular.
Often confused with
Sassolite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside sassolite
Minerals reported to co-occur with sassolite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- H₃BO₃
- Mohs hardness
- 1
- Density
- 1.46-1.50 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Encrustations, platy, tabular
- Cleavage
- Perfect on {001}, micaceous
- Fluorescence
- Blue under SW UV
- Rarity
- Uncommon
- Uses
- Collector, Chemical industry
- Host rock
- An evaporite or sublimate around hot spring lagoons and volcanic fumaroles; in bedded sedimentary borate deposits
Where rockhounds find sassolite
Classic worldwide localities
- Kramer borate deposit, Boron, Kern Co., in Death Valley, near the head of Furnace Creek, and in the Upper Biddy mine, near Ryan, Inyo Co., and at The Geysers, Sonoma Co., California, USA
- Norris geyser basin, Yellowstone National Park, Wyoming, USA
- Steamboat Hot Springs, Steamboat Springs district, Washoe Co., Nevada, USA
- Tuscany, around the lagoons at Sasso, eight km from Castelnuovo, Val di Cecina, also at Larderello, Italy
- Campi Flegrei, near Naples, and on Vesuvius, Campania, Italy
- Vulcano, Lipari Islands, Italy
Field-hunting tip
Where it forms: An evaporite or sublimate around hot spring lagoons and volcanic fumaroles; in bedded sedimentary borate deposits. If you start seeing larderellite, santite, ginorite in float, you are in the right ground. Typical habit: encrustations, platy, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify sassolite?+
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What rocks look like sassolite?+
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Find sassolite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
