Woodruffite is a rare manganese zinc oxide mineral often found as dark, earthy, or botryoidal crusts in oxidized zones of ore deposits. It is most notable for its historical occurrence in the famous zinc-manganese mines of Franklin and Sterling Hill, New Jersey. Collectors should look for its distinctive brownish streak and association with other rare zinc minerals.
Is this woodruffite?
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 woodruffite with a known reference. Woodruffite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Woodruffite leaves a brown streak.
- 3Read the lusterHold the specimen under a strong light. Woodruffite typically shows a dull luster.
- 4Match the color rangeCompare against the expected color range: dark brown, black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: botryoidal, massive, or as earthy coatings.
Often confused with
Woodruffite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Romanèchite is the harder of the two (Mohs 5-6 vs. 2); streak differs — Woodruffite leaves brown, Romanèchite leaves shiny brownish black; luster reads dull on Woodruffite and submetallic to dull on Romanèchite.
How to tell apart: Hausmannite is the harder of the two (Mohs 5-5.5 vs. 2); streak differs — Woodruffite leaves brown, Hausmannite leaves brownish-red; luster reads dull on Woodruffite and submetallic on Hausmannite.
How to tell apart: Lithiophorite is the harder of the two (Mohs 3 vs. 2); streak differs — Woodruffite leaves brown, Lithiophorite leaves black; luster reads dull on Woodruffite and submetallic on Lithiophorite.
Often found alongside woodruffite
Minerals reported to co-occur with woodruffite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Zn,Mn²⁺)Mn⁴⁺₃O₇·1-2H₂O
- Mohs hardness
- 2
- Density
- 3.3-3.6 g/cm³
- Colors
- Streak
- Brown
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Botryoidal, Massive, Or as Earthy Coatings
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Metamorphosed Zinc-manganese Ore Deposits
- Typical price
- $20-150 per specimen depending on size and quality
Where rockhounds find woodruffite
Classic worldwide localities
- Sterling Hill Mine, New Jersey, USA
- Franklin Mine, New Jersey, USA
Field-hunting tip
Look in metamorphosed zinc-manganese ore deposits country — that is the host setting where woodruffite typically forms. If you start seeing willemite, franklinite, zincite in float, you are in the right ground. Field specimens usually show a botryoidal, massive, or as earthy coatings habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find woodruffite on the map
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