Chalcomenite is a rare copper selenite mineral that forms striking bright blue, prismatic crystals. It is typically found as a secondary mineral in the oxidation zones of selenium-rich ore deposits, often appearing as crusts or small crystal clusters.
Is this chalcomenite?
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 chalcomenite with a known reference. Chalcomenite sits at Mohs 2-2.5, 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: light blue.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: short prismatic crystals, crusts, radial aggregates.
Often confused with
Chalcomenite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Azurite is the harder of the two (Mohs 3.5-4 vs. 2-2.5); streak differs, so Chalcomenite leaves light blue, Azurite leaves pale blue.
How to tell apart: Streak differs, so Chalcomenite leaves light blue, Chalcanthite leaves white.
Often found alongside chalcomenite
Minerals reported to co-occur with chalcomenite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CuSeO₃·2H₂O
- Mohs hardness
- 2-2.5
- Density
- 3.35 g/cm³
- Colors
- Streak
- Light blue
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Short prismatic crystals, crusts, radial aggregates
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral in oxidized Cu–Se-bearing deposits
Where rockhounds find chalcomenite
Classic worldwide localities
- Middlemarch mine, near Pearce, Cochise Co., Arizona, USA
- Majuba Hill, Pershing Co., Nevada, USA
- Bozo No. 1 claim, Skull Creek, Moffat Co., Colorado, USA
- Cerro de Cacheuta, Mendoza Province, and at the Cóndor mine, Los Llantenes district, Sierra de Cacheuta, in the Sierra de Umango and Sierra de Famatina, La Rioja Province, Argentina
- Pacajake mine, Hiaco, 24 km east-northeast of Colquechaca, and in the El Dragón mine, 30 km southwest of Cerro Rico de Potosí, Potosí, Bolivia
- Eagle shaft, Beaverlodge Lake, near Uranium City, Saskatchewan, Canada
Field-hunting tip
Where it forms: A rare secondary mineral in oxidized Cu–Se-bearing deposits. If you start seeing umangite, clausthalite, molybdomenite in float, you are in the right ground. Typical habit: short prismatic crystals, crusts, radial aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
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Find chalcomenite on the map
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