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. Kempite leaves a pale green streak.
- 3Read the lusterHold the specimen under a strong light. Kempite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: emerald-green, olive-green.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: granular, massive, thin crusts.
Often confused with
Kempite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Kempite leaves pale 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 8 vs. 3.5); streak differs — Kempite leaves pale 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
- 3.2 g/cm³
- Colors
- Streak
- Pale Green
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Granular, Massive, Thin Crusts
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Manganese Deposits in Chert
- Typical price
- $50-300 per specimen
Where rockhounds find kempite
Classic worldwide localities
- Alum Rock Park, San Jose, California, USA
Field-hunting tip
Look in manganese deposits in chert country — that is the host setting where kempite typically forms. If you start seeing hausmannite, neotocite, rhodochrosite in float, you are in the right ground. Field specimens usually show a granular, massive, thin crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify kempite?+
Where is kempite found?+
How much is kempite worth?+
What rocks look like kempite?+
What minerals are found with kempite?+
What kind of rock does kempite form in?+
What is kempite used for?+
Find kempite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
