Boussingaultite is a rare ammonium magnesium sulfate that typically forms as a white, crusty efflorescence in geothermal regions or burning coal waste piles. Collectors usually find it as delicate coatings or powdery aggregates, as it is highly soluble in water and unstable in high humidity. Careful storage in a dry, airtight environment is essential to prevent degradation.
Is this boussingaultite?
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 boussingaultite with a known reference. Boussingaultite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Boussingaultite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Boussingaultite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, yellowish, gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: crusts, efflorescences, granular, sometimes small prismatic crystals.
Often confused with
Boussingaultite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside boussingaultite
Minerals reported to co-occur with boussingaultite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (NH₄)₂Mg(SO₄)₂·6H₂O
- Mohs hardness
- 2
- Density
- 1.73 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Crusts, Efflorescences, Granular, Sometimes Small Prismatic Crystals
- Cleavage
- Distinct On {010}
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Fumaroles, Burning Coal Mine Dumps, Geothermal Areas
- Typical price
- $10-60 for small specimens
Where rockhounds find boussingaultite
Classic worldwide localities
- Tuscany, Italy
- Almadén, Spain
- Cerro Pintado, Chile
- Gisburn, England
Field-hunting tip
Look in fumaroles, burning coal mine dumps, geothermal areas country — that is the host setting where boussingaultite typically forms. If you start seeing alunogen, tschermigite, gypsum in float, you are in the right ground. Field specimens usually show a crusts, efflorescences, granular, sometimes small prismatic crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify boussingaultite?+
Where is boussingaultite found?+
How much is boussingaultite worth?+
What rocks look like boussingaultite?+
What minerals are found with boussingaultite?+
What kind of rock does boussingaultite form in?+
What is boussingaultite used for?+
Find boussingaultite on the map
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