Kempite is an extremely rare manganese chloride hydroxide typically found as small, vibrant emerald-green grains or crusts. It is most famous for its occurrence in the manganese-rich deposits of California's Alum Rock Park, where it forms in association with other manganese minerals.
Is this kempite?
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 kempite with a known reference. Kempite sits at Mohs ~3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light green.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: emerald green.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: crystalline, prismatic.
Often confused with
Kempite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Kempite leaves light green, Atacamite leaves apple-green; luster reads vitreous on Kempite and adamantine to vitreous on Atacamite.
How to tell apart: Lawsonite is the harder of the two (Mohs 6 vs. ~3.5); streak differs, so Kempite leaves light green, Lawsonite leaves white.
Often found alongside kempite
Minerals reported to co-occur with kempite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn₂Cl(OH)₃
- Mohs hardness
- ~3.5
- Density
- 2.94 g/cm³
- Colors
- Streak
- Light green
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Orthorhombic
- Crystal habit
- Crystalline, prismatic
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In an erratic boulder with other manganese-bearing species
Where rockhounds find kempite
Classic worldwide localities
- Alum Rock Canyon, eight km east of San Jose, Santa Clara Co., California, USA
Field-hunting tip
Where it forms: In an erratic boulder with other manganese-bearing species. If you start seeing pyrochroite, hausmannite, rhodochrosite in float, you are in the right ground. Typical habit: crystalline, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify kempite?+
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What rocks look like kempite?+
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Find kempite on the map
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