Riomarinaite is a very rare hydrated iron sulfate mineral discovered in the mines of Elba Island. It typically occurs as delicate, pearly-white platy crystals or radial clusters formed as a secondary alteration product of pyrite. Collectors prize it for its rarity and its association with the classic mineral localities of Tuscany.
Is this riomarinaite?
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 riomarinaite with a known reference. Riomarinaite 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. Riomarinaite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Riomarinaite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: platy crystals, radial aggregates.
Often confused with
Riomarinaite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Riomarinaite leaves white, Jarosite leaves yellow; luster reads pearly on Riomarinaite and vitreous on Jarosite.
How to tell apart: Streak differs — Riomarinaite leaves white, Copiapite leaves yellow.
Often found alongside riomarinaite
Minerals reported to co-occur with riomarinaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaFe³⁺(SO₄)₂·H₂O
- Mohs hardness
- 2
- Density
- 2.16 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Platy Crystals, Radial Aggregates
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Mineral Deposits
- Typical price
- $20-100 for small thumbnail specimens
Where rockhounds find riomarinaite
Classic worldwide localities
- Rio Marina, Elba Island, Italy
Field-hunting tip
Look in hydrothermal mineral deposits country — that is the host setting where riomarinaite typically forms. If you start seeing pyrite, hematite, coquimbite in float, you are in the right ground. Field specimens usually show a platy crystals, radial aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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What rocks look like riomarinaite?+
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Find riomarinaite on the map
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