Cobaltarthurite is a rare secondary mineral formed in the oxidized zones of cobalt-rich hydrothermal deposits. It typically appears as striking blue or blue-green acicular crystal sprays or coatings associated with other arsenate minerals.
Is this cobaltarthurite?
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 cobaltarthurite with a known reference. Cobaltarthurite 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. Cobaltarthurite leaves a light blue streak.
- 3Read the lusterHold the specimen under a strong light. Cobaltarthurite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: blue, blue-green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular to prismatic crystals, often as radial sprays or crusts.
Often confused with
Cobaltarthurite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside cobaltarthurite
Minerals reported to co-occur with cobaltarthurite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CoFe₂³⁺(AsO₄)₂(OH)₂·4H₂O
- Mohs hardness
- 3
- Density
- 3.5 g/cm³
- Colors
- Streak
- Light Blue
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular to Prismatic Crystals, Often as Radial Sprays or Crusts
- Cleavage
- None Observed
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Hydrothermal Cobalt-arsenic Deposits
- Typical price
- $50-300 per specimen
Where rockhounds find cobaltarthurite
Classic worldwide localities
- Jáchymov, Czech Republic
- Schneeberg, Germany
- Bou Azzer, Morocco
Field-hunting tip
Look in oxidized zones of hydrothermal cobalt-arsenic deposits country — that is the host setting where cobaltarthurite typically forms. If you start seeing skutterudite, erythrite, pharmacolite in float, you are in the right ground. Field specimens usually show a acicular to prismatic crystals, often as radial sprays or crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find cobaltarthurite on the map
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