Coombsite is a rare phyllosilicate mineral typically found in metamorphosed zinc-rich deposits. It is best identified by its brownish platy appearance, which often forms dense, micaceous aggregates associated with other rare zinc minerals.
Is this coombsite?
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 coombsite with a known reference. Coombsite 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. Streak: brownish yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: brown.
- 5Look at form & habitCrystal system: trigonal. Typical habit: platy aggregates.
Often confused with
Coombsite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Coombsite leaves brownish yellow, Serpentine leaves white; luster reads vitreous on Coombsite and greasy on Serpentine.
How to tell apart: Streak differs, so Coombsite leaves brownish yellow, Clinochlore leaves greenish white to white; luster reads vitreous on Coombsite and pearly, greasy, dull on Clinochlore.
Often found alongside coombsite
Minerals reported to co-occur with coombsite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KMn₁₃(Si,Al)₁₈O₄₂(OH)₁₄
- Mohs hardness
- 2.5
- Density
- 3.0 g/cm³
- Colors
- Streak
- Brownish yellow
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Trigonal
- Crystal habit
- Platy aggregates
- Cleavage
- Good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a manganese-rich rock in metagraywacke-argillite in the pumpellyite-prehnite facies
Where rockhounds find coombsite
Classic worldwide localities
- Watson's Beach, southeastern Otago, New Zealand
Field-hunting tip
Where it forms: In a manganese-rich rock in metagraywacke-argillite in the pumpellyite-prehnite facies. If you start seeing rhodonite, quartz, rhodochrosite in float, you are in the right ground. Typical habit: platy aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
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Find coombsite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
