Bementite is a rare manganese silicate typically found as dense, massive, or foliated aggregates. It is best known to collectors from the famous zinc-manganese mines of Franklin and Sterling Hill, New Jersey, where it is often associated with other rare manganese minerals.
Is this bementite?
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 bementite with a known reference. Bementite sits at Mohs 4.5-6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellow white.
- 3Read the lusterHold the specimen under a strong light. Luster: waxy, pearly on perfect cleavage.
- 4Match the color rangeCompare against the expected color range: brown, gray, yellow, yellow brown, pink.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: massive, radial.
Often confused with
Bementite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Bementite leaves yellow white, Serpentine leaves white; luster reads waxy, pearly on perfect cleavage on Bementite and greasy on Serpentine.
How to tell apart: Streak differs, so Bementite leaves yellow white, Friedelite leaves pale rose; luster reads waxy, pearly on perfect cleavage on Bementite and vitreous, pearly on basal plane on Friedelite.
Often found alongside bementite
Minerals reported to co-occur with bementite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn₇Si₆O₁₅(OH)₈
- Mohs hardness
- 4.5-6
- Density
- 2.98-3.02 g/cm³
- Streak
- Yellow white
- Luster
- Waxy, pearly on perfect cleavage
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Massive, radial
- Cleavage
- Perfect on {100}, {010}, {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Layered parallel to the walls of secondary veins of calcite in a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA); intimately intergrown with other manganese minerals (Olympic Peninsula, Washington, USA)
Where rockhounds find bementite
2 mapped spotsClassic worldwide localities
- Franklin, Sussex Co., New Jersey, USA
- Olympic Peninsula, an ore mineral at a number of Clallan, Jefferson, and Mason Cos., Washington, USA
- Ray, Pinal Co., Arizona, USA
- Hale Creek, Trinity Co., California, USA
- Treburland mine, Altarnun, Cornwall, and near Chillaten, Devon, England
- Langbån, Värmland, Sweden
Field-hunting tip
Where it forms: Layered parallel to the walls of secondary veins of calcite in a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA); intimately intergrown with other manganese minerals (Olympic Peninsula, Washington, USA). If you start seeing calcite, willemite, hausmannite in float, you are in the right ground. Typical habit: massive, radial. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in California. Start trip planning there.
Common questions
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Find bementite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
