Mcbirneyite is an extremely rare copper vanadate mineral originally discovered as crusts and small platy crystals in the fumaroles of the Izalco Volcano. Collectors prize it for its vibrant deep blue color, though it is difficult to acquire due to its limited type locality and fragile nature.
Is this mcbirneyite?
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 mcbirneyite with a known reference. Mcbirneyite sits at Mohs 2.5-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: grayish black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: black, dark gray.
- 5Look at form & habitCrystal system: triclinic. Typical habit: platy crystals, crusts, powdery coatings.
Often confused with
Mcbirneyite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Mcbirneyite leaves grayish black, Chalcanthite leaves white; luster reads metallic on Mcbirneyite and vitreous to resinous on Chalcanthite.
How to tell apart: Cuprosklodowskite is the harder of the two (Mohs 4 vs. 2.5-3); streak differs, so Mcbirneyite leaves grayish black, Cuprosklodowskite leaves greenish yellow; luster reads metallic on Mcbirneyite and dull to silky in aggregates on Cuprosklodowskite.
Often found alongside mcbirneyite
Minerals reported to co-occur with mcbirneyite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₃(VO₄)₂
- Mohs hardness
- 2.5-3
- Density
- 4.50 g/cm³
- Streak
- Grayish black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Triclinic
- Crystal habit
- Platy crystals, crusts, powdery coatings
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Very rare in the sulfate zone of sublimates around a fumarole in a composite volcano, likely formed between 100°C–200°C
Where rockhounds find mcbirneyite
Classic worldwide localities
- Izalco Volcano, El Salvador
Field-hunting tip
Where it forms: Very rare in the sulfate zone of sublimates around a fumarole in a composite volcano, likely formed between 100°C–200°C. If you start seeing fingerite, thenardite, euchlorine in float, you are in the right ground. Typical habit: platy crystals, crusts, powdery coatings. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify mcbirneyite?+
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Is mcbirneyite safe to handle?+
What rocks look like mcbirneyite?+
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Find mcbirneyite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
