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 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Callaghanite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Callaghanite 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: 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 — Callaghanite leaves white, Malachite leaves light green.
How to tell apart: Streak differs — Callaghanite leaves white, Azurite leaves light blue; luster reads vitreous on Callaghanite and vitreous to dull on Azurite.
How to tell apart: Callaghanite is noticeably harder (Mohs 3 vs. 2); streak differs — Callaghanite leaves white, Aurichalcite leaves pale blue; luster reads vitreous on Callaghanite and 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
- Cu₄Mg₄(CO₃)₃(OH)₁₈·2H₂O
- Mohs hardness
- 3
- Density
- 2.47 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Platy Crystals, Crusts, Radial Aggregates
- Cleavage
- Perfect On {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Altered Magnesium-rich Rocks, Hydrothermal Alteration Zones
- Typical price
- $50-300 per specimen
Where rockhounds find callaghanite
Classic worldwide localities
- Gabbs, Nevada, USA
- Långban, Sweden
Field-hunting tip
Look in altered magnesium-rich rocks, hydrothermal alteration zones country — that is the host setting where callaghanite typically forms. If you start seeing magnesite, brucite, hydromagnesite in float, you are in the right ground. Field specimens usually show a platy crystals, crusts, radial aggregates habit, so 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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