Rosenbergite is a rare aluminum fluoride hydrate mineral primarily found as a sublimation product in fumaroles. It typically occurs as small, colorless to white prismatic crystals and is noted for its relative softness and specific formation environment.
Is this rosenbergite?
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 rosenbergite with a known reference. Rosenbergite sits at Mohs 3-3.5, 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: vitreous.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: prismatic crystals.
Often confused with
Rosenbergite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside rosenbergite
Minerals reported to co-occur with rosenbergite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- AlF₃·3H₂O
- Mohs hardness
- 3-3.5
- Density
- 2.10 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Tetragonal
- Crystal habit
- Prismatic crystals
- Cleavage
- {001}, good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Very rare in cavities in a silicified limestone from an antimony deposit in highly silicified evaporites (Cetine mine, Italy); in volcanic sublimates (Mt. Erebus, Antarctica)
Where rockhounds find rosenbergite
Classic worldwide localities
- Cetine mine, 20 km southwest of Siena, Tuscany, Italy
- Mt. Erebus, Antarctica
Field-hunting tip
Where it forms: Very rare in cavities in a silicified limestone from an antimony deposit in highly silicified evaporites (Cetine mine, Italy); in volcanic sublimates (Mt. Erebus, Antarctica). If you start seeing gypsum, fluorite, elpasolite in float, you are in the right ground. Typical habit: prismatic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify rosenbergite?+
Where is rosenbergite found?+
What rocks look like rosenbergite?+
What minerals are found with rosenbergite?+
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Find rosenbergite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
