Callaghanite is a rare copper-magnesium carbonate mineral typically found as small, vibrant blue to blue-green platy crystals. It is highly sought after by mineral collectors, specifically occurring in altered brucite-magnesite deposits where it forms as a secondary mineral.
Is this callaghanite?
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 callaghanite with a known reference. Callaghanite sits at Mohs 3-3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: azure, violet blue.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: platy crystals, crusts, radial aggregates.
Often confused with
Callaghanite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Callaghanite leaves white, Malachite leaves pale green; luster reads vitreous on Callaghanite and adamantine to vitreous; silky if fibrous; dull to earthy if massive on Malachite.
How to tell apart: Streak differs, so Callaghanite leaves white, Azurite leaves pale blue.
How to tell apart: Callaghanite is noticeably harder (Mohs 3-3.5 vs. 1-2); streak differs, so Callaghanite leaves white, Aurichalcite leaves light blue; luster reads vitreous on Callaghanite and silky to pearly on Aurichalcite.
Often found alongside callaghanite
Minerals reported to co-occur with callaghanite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₂Mg₂CO₃(OH)₆·2H₂O
- Mohs hardness
- 3-3.5
- Density
- 2.71 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Platy crystals, crusts, radial aggregates
- Cleavage
- On {111} and {111}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Disseminated in the contact zone between diorite and serpentinized dolostone
Where rockhounds find callaghanite
Classic worldwide localities
- Gabbs, Gabbs district, Nye Co., Nevada, USA (type locality)
Field-hunting tip
Where it forms: Disseminated in the contact zone between diorite and serpentinized dolostone. If you start seeing magnesite, dolomite, serpentine in float, you are in the right ground. Typical habit: platy crystals, crusts, radial aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
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Find callaghanite on the map
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