Thermessaite is a rare potassium aluminum fluoride mineral typically found in volcanic fumaroles. It most commonly occurs as small, colorless, tabular crystals associated with other halide minerals in high-temperature environments.
Is this thermessaite?
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 thermessaite with a known reference. Thermessaite 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: colorless, white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic.
Often confused with
Thermessaite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside thermessaite
Minerals reported to co-occur with thermessaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₂AlF₃(SO₄)
- Mohs hardness
- 2
- Density
- 2.77 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In altered pyroclastic breccias in an active fumarole (300-350° C)
Where rockhounds find thermessaite
Classic worldwide localities
- La Fossa crater, Vulcano, Aeolian Islands, Sicily, Italy
Field-hunting tip
Where it forms: In altered pyroclastic breccias in an active fumarole (300-350° C). If you start seeing alunite, sassolite, anhydrite in float, you are in the right ground. Typical habit: prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify thermessaite?+
Where is thermessaite found?+
Is thermessaite safe to handle?+
What rocks look like thermessaite?+
What minerals are found with thermessaite?+
What kind of rock does thermessaite form in?+
What is thermessaite used for?+
Find thermessaite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
