Bassanite is a rare calcium sulfate mineral often found as an dehydration product of gypsum in volcanic fumaroles or arid evaporite environments. It typically occurs as white fibrous or powdery coatings and is structurally related to the industrial material known as plaster of Paris.
Is this bassanite?
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 bassanite with a known reference. Bassanite sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Bassanite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Bassanite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, gray, yellowish.
- 5Look at form & habitCrystal system: trigonal. Typical habit: fibrous, massive, powdery crusts.
Often confused with
Bassanite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside bassanite
Minerals reported to co-occur with bassanite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaSO₄·0.5H₂O
- Mohs hardness
- 3
- Density
- 2.76 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Fibrous, Massive, Powdery Crusts
- Cleavage
- Good
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Volcanic Fumaroles, Evaporite Deposits
- Typical price
- $20-100 per specimen
Where rockhounds find bassanite
1 mapped spotsClassic worldwide localities
- Vesuvius, Italy
- Etna, Sicily
- various evaporite deposits
Field-hunting tip
Look in volcanic fumaroles, evaporite deposits country — that is the host setting where bassanite typically forms. If you start seeing gypsum, anhydrite, sulfur in float, you are in the right ground. Field specimens usually show a fibrous, massive, powdery crusts 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 bassanite?+
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Find bassanite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
