Rostite is a rare aluminum sulfate-fluoride hydrate that frequently forms as efflorescences or delicate crystal sprays on coal mine waste heaps. Because it is highly soluble and fragile, specimens should be stored in dry, airtight containers to prevent dehydration and crumbling. It is primarily sought by advanced mineral collectors specializing in secondary sulfate minerals.
Is this rostite?
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 rostite with a known reference. Rostite 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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: earthy, massive.
Often confused with
Rostite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside rostite
Minerals reported to co-occur with rostite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- AlSO₄(OH)·5H₂O
- Mohs hardness
- 2
- Density
- 1.892 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Orthorhombic
- Crystal habit
- Earthy, massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In burning waste heaps at a coal mine, formed by decomposition of aluminum-bearing rocks by gasses containing SO2 and fluorine (Libušín, Czech Republic)
Where rockhounds find rostite
Classic worldwide localities
- Nejedlý I (Schoeller) coal mine, Libušín, near Kladno, Czech Republic
- Cetine mine, 20 km southwest of Siena, Tuscany, Italy
Field-hunting tip
Where it forms: In burning waste heaps at a coal mine, formed by decomposition of aluminum-bearing rocks by gasses containing SO2 and fluorine (Libušín, Czech Republic). If you start seeing tschermigite, alunogen, copiapite in float, you are in the right ground. Typical habit: earthy, massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify rostite?+
Where is rostite found?+
What rocks look like rostite?+
What minerals are found with rostite?+
What kind of rock does rostite form in?+
What is rostite used for?+
Find rostite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
