Gageite is a rare manganese silicate typically found as delicate acicular crystals or radial sprays within metamorphosed zinc deposits. It is most famous from the historic mines of the Franklin Mining District in New Jersey, where it is highly prized by mineral collectors for its elegant crystalline habit.
Is this gageite?
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 gageite with a known reference. Gageite 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: white.
- 3Read the lusterHold the specimen under a strong light. Luster: highly vitreous.
- 4Match the color rangeCompare against the expected color range: pink, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: radial.
Often confused with
Gageite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Manganosite is the harder of the two (Mohs 5.5 vs. 3); streak differs, so Gageite leaves white, Manganosite leaves brown; luster reads highly vitreous on Gageite and vitreous to adamantine, dull on exposure on Manganosite.
How to tell apart: Willemite is the harder of the two (Mohs 5.5 vs. 3); luster reads highly vitreous on Gageite and vitreous to resinous on Willemite.
How to tell apart: Hodgkinsonite is the harder of the two (Mohs <5 vs. 3); luster reads highly vitreous on Gageite and vitreous on Hodgkinsonite.
Often found alongside gageite
Minerals reported to co-occur with gageite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn₂₁Si₈O₂₇(OH)₂₀
- Mohs hardness
- 3
- Density
- 3.46-3.584 g/cm³
- Streak
- White
- Luster
- Highly vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Radial
- Cleavage
- {110}, pronounced
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A late-stage low- to medium-temperature mineral, implanted on other species in fissures and solution cavities, in a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA)
Where rockhounds find gageite
Classic worldwide localities
- Franklin, Sussex Co., New Jersey, and in the Pennsylvania mine, San Antonio Valley, Santa Clara Co., California, USA
- Wessels and N'Chwaning II mines, near Kuruman, Cape Province, South Africa
Field-hunting tip
Where it forms: A late-stage low- to medium-temperature mineral, implanted on other species in fissures and solution cavities, in a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA). If you start seeing zincite, willemite, pyrochroite in float, you are in the right ground. Typical habit: radial. Train your eye for that shape before scanning the outcrop.
Common questions
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Find gageite on the map
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