Coalingite is a rare magnesium-iron carbonate hydroxide mineral typically found as small, golden-yellow to orange-brown plates within serpentinized rocks. Collectors primarily find it as thin coatings or small, micaceous patches in association with other serpentine minerals and brucite. It is most famous for its occurrences in the New Idria district of California.
Is this coalingite?
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 coalingite with a known reference. Coalingite sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Coalingite leaves a yellow streak.
- 3Read the lusterHold the specimen under a strong light. Coalingite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: yellow, orange, brown.
- 5Look at form & habitCrystal system: trigonal. Typical habit: platy, micaceous, massive, or as veinlets.
Often confused with
Coalingite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Coalingite leaves yellow, Pyroaurite leaves white.
How to tell apart: Streak differs — Coalingite leaves yellow, Hydrotalcite leaves white.
How to tell apart: Streak differs — Coalingite leaves yellow, Brucite leaves white.
Often found alongside coalingite
Minerals reported to co-occur with coalingite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mg₁₀Fe₃(OH)₂₄CO₃·2H₂O
- Mohs hardness
- 2.5
- Density
- 2.1 g/cm³
- Streak
- Yellow
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Platy, Micaceous, Massive, Or as Veinlets
- Cleavage
- Perfect Basal
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Serpentinite
- Typical price
- $20-100 per specimen
Where rockhounds find coalingite
Classic worldwide localities
- New Idria Mine, California, USA
- Jeffrey Mine, Quebec, Canada
- Woodsreef, New South Wales, Australia
Field-hunting tip
Look in serpentinite country — that is the host setting where coalingite typically forms. If you start seeing serpentine, magnetite, brucite in float, you are in the right ground. Field specimens usually show a platy, micaceous, massive, or as veinlets habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find coalingite on the map
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