Isselite is a rare copper sulfate, typically blue. It is a late-stage, secondary phase in a Fe-Ni-Co sulfide deposit. It was first described from Lagoscuro mine, Ceranesi, Genoa Province, Liguria, Italy.
Is this isselite?
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 isselite with a known reference. Isselite 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: light blue.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: blue.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: platy crystals, crusts.
Often confused with
Isselite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Isselite leaves light blue, Coquimbite leaves white.
How to tell apart: Streak differs, so Isselite leaves light blue, Fibroferrite leaves white; luster reads vitreous on Isselite and pearly, silky in aggregates on Fibroferrite.
Often found alongside isselite
Minerals reported to co-occur with isselite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₆(SO₄)(OH)₁₀(H₂O)₄·H₂O
- Mohs hardness
- 2.5
- Density
- 3.00 g/cm³
- Colors
- Streak
- Light blue
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Platy crystals, crusts
- Cleavage
- Good on {001} and {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- oxidized ore deposits
Where rockhounds find isselite
Classic worldwide localities
- Lagoscuro mine, Liguria, Italy
Field-hunting tip
Where it forms: oxidized ore deposits. If you start seeing jarosite, melanterite, copiapite in float, you are in the right ground. Typical habit: platy crystals, crusts. Train your eye for that shape before scanning the outcrop.
Common questions
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Find isselite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
