Rossiantonite is a rare hydrous aluminum sulfate mineral typically occurring as fragile, fibrous white crusts or efflorescences in mine environments. It is a secondary mineral formed through the oxidation of sulfides, often found in association with other sulfate minerals in abandoned mine workings. Due to its solubility and delicate nature, it is primarily of interest to advanced micromineral collectors.
Is this rossiantonite?
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 rossiantonite with a known reference. Rossiantonite 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. Rossiantonite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Rossiantonite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: white, pale yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous aggregates.
Often confused with
Rossiantonite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside rossiantonite
Minerals reported to co-occur with rossiantonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₄(SO₄)(OH)₁₀·5H₂O
- Mohs hardness
- 2
- Density
- 1.98 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous Aggregates
- Cleavage
- Perfect in One Direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Mining Waste Dumps and Altered Argillaceous Rocks
- Typical price
- $50-300 per specimen
Where rockhounds find rossiantonite
Classic worldwide localities
- Rossi mine, Italy
- Tuscany, Italy
Field-hunting tip
Look in mining waste dumps and altered argillaceous rocks country — that is the host setting where rossiantonite typically forms. If you start seeing alunogen, gypsum, pickeringite in float, you are in the right ground. Field specimens usually show a fibrous aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify rossiantonite?+
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What rocks look like rossiantonite?+
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Find rossiantonite on the map
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