Franklinfurnaceite is a rare phyllosilicate mineral uniquely found in the zinc ore bodies of Franklin and Ogdensburg, New Jersey. It typically occurs as small, dark brown to black platy crystals associated with other classic Franklin minerals like willemite and zincite. Collectors prize it for its specific occurrence and distinct, mica-like crystalline structure.
Is this franklinfurnaceite?
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 franklinfurnaceite with a known reference. Franklinfurnaceite 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. Franklinfurnaceite leaves a brown streak.
- 3Read the lusterHold the specimen under a strong light. Franklinfurnaceite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: dark brown, black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: platy crystals.
Often found alongside franklinfurnaceite
Minerals reported to co-occur with franklinfurnaceite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂Fe³⁺Mn³⁺ZnMn²⁺₂(Si₂O₇)(OH)₂
- Mohs hardness
- 3
- Density
- 3.37 g/cm³
- Colors
- Streak
- Brown
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Platy Crystals
- Cleavage
- Perfect On {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphosed Zinc Ore Deposits
- Typical price
- $50-500 thumbnail, $300-1500 cabinet
Where rockhounds find franklinfurnaceite
Classic worldwide localities
- Franklin Mine, New Jersey, USA
- Sterling Hill Mine, New Jersey, USA
Field-hunting tip
Look in metamorphosed zinc ore deposits country — that is the host setting where franklinfurnaceite typically forms. If you start seeing willemite, franklinite, zincite in float, you are in the right ground. Field specimens usually show a platy crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find franklinfurnaceite on the map
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