Gerstmannite is a rare silicate mineral found exclusively in the Franklin mining district of New Jersey. It typically occurs as small, pale pink to colorless prismatic crystals or as granular masses associated with willemite and zincite.
Is this gerstmannite?
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 gerstmannite with a known reference. Gerstmannite sits at Mohs 6 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Gerstmannite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Gerstmannite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: pink, white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic crystals, massive, granular.
Often confused with
Gerstmannite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside gerstmannite
Minerals reported to co-occur with gerstmannite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Mg,Mn)₂Zn(SiO₄)(OH)₂
- Mohs hardness
- 6
- Density
- 3.83 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic Crystals, Massive, Granular
- Cleavage
- Distinct On {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphosed Zinc Ore Deposits
- Typical price
- $50-500 depending on specimen size and clarity
Where rockhounds find gerstmannite
Classic worldwide localities
- Franklin, New Jersey, USA
Field-hunting tip
Look in metamorphosed zinc ore deposits country — that is the host setting where gerstmannite typically forms. If you start seeing willemite, franklinite, zincite in float, you are in the right ground. Field specimens usually show a prismatic crystals, massive, granular habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find gerstmannite on the map
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