Marthozite is a rare copper selenium oxysalt typically found as vivid green, transparent, tabular crystals. It is primarily associated with the oxidized zones of selenium-rich uranium deposits, most famously in the Katanga region of the DR Congo. Collectors often look for its diagnostic radiating habit and distinctive association with other rare secondary selenium minerals.
Is this marthozite?
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 marthozite with a known reference. Marthozite sits at Mohs 6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: greenish brown, yellow green.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: bladed.
Often confused with
Marthozite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Marthozite is noticeably harder (Mohs 6 vs. 2-3); luster reads vitreous on Marthozite and adamantine on Derriksite.
How to tell apart: Marthozite is noticeably harder (Mohs 6 vs. 3-4); streak differs, so Marthozite leaves pale yellow, Demesmaekerite leaves yellowish.
Often found alongside marthozite
Minerals reported to co-occur with marthozite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu(UO₂)₃(SeO₃)₂O₂·8H₂O
- Mohs hardness
- 6
- Density
- 4.4 g/cm³
- Streak
- Pale yellow
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Orthorhombic
- Crystal habit
- Bladed
- Cleavage
- Perfect on {100}; imperfect on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare alteration product of selenian digenite in the oxidation zone of a uranium-bearing Cu-Co hydrothermal ore deposit
Where rockhounds find marthozite
Classic worldwide localities
- Musonoi Co-Cu mine, near Kolwezi, Katanga Province, Congo (Shaba Province, Zaire)
Field-hunting tip
Where it forms: A rare alteration product of selenian digenite in the oxidation zone of a uranium-bearing Cu-Co hydrothermal ore deposit. If you start seeing digenite, demesmaekerite, denningite in float, you are in the right ground. Typical habit: bladed. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify marthozite?+
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Is marthozite safe to handle?+
What rocks look like marthozite?+
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Find marthozite on the map
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