Hilarionite is a very rare iron sulfate mineral typically found as earthy, pale green coatings in oxidized ore zones. It was first described from the historic mines of the Laurion district in Greece. Collectors prize it for its unique chemical composition and restricted locality occurrences.
Is this hilarionite?
4-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 hilarionite with a known reference. Hilarionite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Read the lusterHold the specimen under a strong light. Luster: vitreous to silky.
- 3Match the color rangeCompare against the expected color range: yellowish green.
- 4Look at form & habitCrystal system: monoclinic. Typical habit: crusts, aggregates, earthy.
Often confused with
Hilarionite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads vitreous to silky on Hilarionite and subadamantine to vitreous, resinous on fractures on Jarosite.
How to tell apart: Luster reads vitreous to silky on Hilarionite and pearly on {010} on Copiapite.
Often found alongside hilarionite
Minerals reported to co-occur with hilarionite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₂(SO₄)(AsO₄)(OH)·6H₂O
- Mohs hardness
- 2
- Density
- 2.40 g/cm³
- Colors
- Luster
- Vitreous to silky
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Crusts, aggregates, earthy
- Cleavage
- Good parallel to elongation
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral in the oxidized zone of a sulfide-rich (pyrite, sphalerite, chalcopyrite, galena) orebody
Where rockhounds find hilarionite
Classic worldwide localities
- Hilarion mine, near Agios Konstantinos (Kamariza), Lavrion ore district, Atliki Prefecture, Greece
Field-hunting tip
Where it forms: A secondary mineral in the oxidized zone of a sulfide-rich (pyrite, sphalerite, chalcopyrite, galena) orebody. If you start seeing goethite, gypsum, bukovskyite in float, you are in the right ground. Typical habit: crusts, aggregates, earthy. Train your eye for that shape before scanning the outcrop.
Common questions
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Find hilarionite on the map
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