Ramsdellite is a manganese oxide mineral typically found as metallic, black prismatic to needle-like crystals or massive, fibrous aggregates. It is often confused with pyrolusite, though it is usually distinguished by its orthorhombic structure and distinct cleavage. Collectors primarily seek out well-defined bladed crystals from famous historical manganese localities.
Is this ramsdellite?
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 ramsdellite with a known reference. Ramsdellite sits at Mohs ~3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black, may have brownish tint.
- 3Read the lusterHold the specimen under a strong light. Luster: brilliant metallic.
- 4Match the color rangeCompare against the expected color range: black, iron black, steel gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: granular, massive, platy.
Often confused with
Ramsdellite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads brilliant metallic on Ramsdellite and metallic on Pyrolusite.
How to tell apart: Nsutite is the harder of the two (Mohs 6.5-8.5 vs. ~3); luster reads brilliant metallic on Ramsdellite and metallic to earthy on Nsutite.
How to tell apart: Manganite is the harder of the two (Mohs 4 vs. ~3); streak differs, so Ramsdellite leaves black, may have brownish tint, Manganite leaves reddish brown to nearly black; luster reads brilliant metallic on Ramsdellite and submetallic on Manganite.
Often found alongside ramsdellite
Minerals reported to co-occur with ramsdellite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MnO₂
- Mohs hardness
- ~3
- Density
- 4.65-4.83 g/cm³
- Streak
- Black, may have brownish tint
- Luster
- Brilliant metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Granular, massive, platy
- Cleavage
- Prominent, on three pinacoids and a prism
- Rarity
- Uncommon
- Uses
- Collector, Ore of manganese
- Host rock
- A secondary mineral in manganese deposits, formed by inversion of pyrolusite or oxidative dehydrogenation of groutite
Where rockhounds find ramsdellite
Classic worldwide localities
- Lake Valley, Sierra Co., New Mexico, USA
- Artillery Mountains, Mohave Co., and at the Mistake mine, Yavapai Co., Arizona, USA
- Idarado mine, near Telluride, San Miguel Co., Colorado, USA
- Monroe-Tener mine, near Chisholm, St. Louis Co., Minnesota, USA
- East River, Pictou Co., Nova Scotia, Canada
- Los Gavilanes, Baja California, Mexico
Field-hunting tip
Where it forms: A secondary mineral in manganese deposits, formed by inversion of pyrolusite or oxidative dehydrogenation of groutite. If you start seeing pyrolusite, hollandite, cryptomelane in float, you are in the right ground. Typical habit: granular, massive, platy. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ramsdellite?+
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What rocks look like ramsdellite?+
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Find ramsdellite on the map
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