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. Streak: brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: dark brown.
- 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
- Ca₂Mn₃MnFeZn₂Si₂O₁₀(OH)₈
- Mohs hardness
- 3
- Density
- 3.66 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
- A late-stage mineral in vugs in a metamorphosed stratiform zinc deposit
Where rockhounds find franklinfurnaceite
Classic worldwide localities
- Franklin, Sussex Co., New Jersey, USA
Field-hunting tip
Where it forms: A late-stage mineral in vugs in a metamorphosed stratiform zinc deposit. If you start seeing willemite, clinohedrite, hodgkinsonite in float, you are in the right ground. Typical habit: platy crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify franklinfurnaceite?+
Where is franklinfurnaceite found?+
What minerals are found with franklinfurnaceite?+
What kind of rock does franklinfurnaceite form in?+
What is franklinfurnaceite used for?+
Find franklinfurnaceite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
