Chlorothionite is a very rare copper-potassium sulfate chloride found almost exclusively in volcanic fumarole environments. It is characterized by its distinct bright blue to blue-green color, typically appearing as delicate crusts or efflorescences around volcanic vents.
Is this chlorothionite?
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 chlorothionite with a known reference. Chlorothionite sits at Mohs 2.5, 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: light blue.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: crusts, granular.
Often confused with
Chlorothionite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside chlorothionite
Minerals reported to co-occur with chlorothionite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₂CuSO₄Cl₂
- Mohs hardness
- 2.5
- Density
- 2.69 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Orthorhombic
- Crystal habit
- Crusts, granular
- Cleavage
- Good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- As sublimates around volcanic fumaroles
Where rockhounds find chlorothionite
Classic worldwide localities
- Vesuvius, Campania, Italy
Field-hunting tip
Where it forms: As sublimates around volcanic fumaroles. If you start seeing tenorite, sylvite, halite in float, you are in the right ground. Typical habit: crusts, granular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify chlorothionite?+
Where is chlorothionite found?+
Is chlorothionite safe to handle?+
What rocks look like chlorothionite?+
What minerals are found with chlorothionite?+
What kind of rock does chlorothionite form in?+
What is chlorothionite used for?+
Find chlorothionite on the map
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