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 3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Marthozite leaves a pale yellow streak.
- 3Read the lusterHold the specimen under a strong light. Marthozite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: green, yellow-green.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals, radiating aggregates, crusts.
Often confused with
Marthozite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Marthozite leaves pale yellow, Derriksite leaves pale green; luster reads vitreous on Marthozite and adamantine on Derriksite.
How to tell apart: Streak differs — 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(SeO₃)₂·2H₂O
- Mohs hardness
- 3
- Density
- 4.9 g/cm³
- Colors
- Streak
- Pale Yellow
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular Crystals, Radiating Aggregates, Crusts
- Cleavage
- Distinct On {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Hydrothermal Selenium-bearing Uranium Deposits
- Typical price
- $100-500 for small microspecimens
Where rockhounds find marthozite
Classic worldwide localities
- Musonoi Mine, Democratic Republic of the Congo
- Shinkolobwe Mine, Democratic Republic of the Congo
Field-hunting tip
Look in oxidized zones of hydrothermal selenium-bearing uranium deposits country — that is the host setting where marthozite typically forms. If you start seeing malachite, derriksite, guilleminite in float, you are in the right ground. Field specimens usually show a tabular crystals, radiating aggregates, crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find marthozite on the map
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