Rhomboclase is a hydrous iron sulfate typically found as an alteration product in the oxidizing zones of sulfide ore deposits. It is best identified by its characteristic tabular, rhombic crystals and its occurrence as secondary crusts or efflorescences in mine workings.
Is this rhomboclase?
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 rhomboclase with a known reference. Rhomboclase 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. Rhomboclase leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Rhomboclase typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, gray, pale blue, pale green.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals, crusts, efflorescences.
Often confused with
Rhomboclase vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside rhomboclase
Minerals reported to co-occur with rhomboclase. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- HFe³⁺(SO₄)₂·4H₂O
- Mohs hardness
- 2
- Density
- 2.05 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular Crystals, Crusts, Efflorescences
- Cleavage
- Perfect On {001}
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Oxidized Zones of Pyrite-bearing Ore Deposits
- Typical price
- $10-50 per specimen
Where rockhounds find rhomboclase
Classic worldwide localities
- Czech Republic
- Germany
- Chile
- USA
Field-hunting tip
Look in oxidized zones of pyrite-bearing ore deposits country — that is the host setting where rhomboclase typically forms. If you start seeing jarosite, copiapite, melanterite in float, you are in the right ground. Field specimens usually show a tabular crystals, crusts, efflorescences habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify rhomboclase?+
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What rocks look like rhomboclase?+
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Find rhomboclase on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
