Kentrolite is a rare lead manganese silicate that typically forms as dark, sub-metallic, radiating prismatic clusters. Collectors most frequently encounter it in specimens from the manganese mines of Sweden or the Franklin mining district in New Jersey. Due to its lead content, it is relatively dense and requires careful handling.
Is this kentrolite?
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 kentrolite with a known reference. Kentrolite sits at Mohs 5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellowish brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to submetallic, greasy, dull.
- 4Match the color rangeCompare against the expected color range: dark reddish brown, reddish black.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: crystalline, prismatic, wheat sheaf.
Often confused with
Kentrolite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Melanotekite is the harder of the two (Mohs 6.5 vs. 5); streak differs, so Kentrolite leaves yellowish brown, Melanotekite leaves greenish gray; luster reads vitreous to submetallic, greasy, dull on Kentrolite and metallic to greasy on Melanotekite.
How to tell apart: Braunite is the harder of the two (Mohs 6-6.5 vs. 5); streak differs, so Kentrolite leaves yellowish brown, Braunite leaves brownish black to steel-gray; luster reads vitreous to submetallic, greasy, dull on Kentrolite and submetallic on Braunite.
How to tell apart: Streak differs, so Kentrolite leaves yellowish brown, Allanite leaves gray; luster reads vitreous to submetallic, greasy, dull on Kentrolite and submetallic on Allanite.
Often found alongside kentrolite
Minerals reported to co-occur with kentrolite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb₂Mn₂Si₂O₉
- Mohs hardness
- 5
- Density
- 6.19 g/cm³
- Streak
- Yellowish brown
- Luster
- Vitreous to submetallic, greasy, dull
- Transparency
- Semitransparent
- Crystal system
- Orthorhombic
- Crystal habit
- Crystalline, prismatic, wheat sheaf
- Cleavage
- Distinct on {110}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a cavity in calcite in a metamorphosed stratiform zinc deposit (Franklin, New Jersey, USA); in veinlets cutting franklinite ore in bedded manganese deposits (Ushkatyn deposits, Kazakhstan)
Where rockhounds find kentrolite
Classic worldwide localities
- Franklin, Sussex Co., New Jersey, USA
- Harstigen mine, near Persberg, Sweden
- Klintgruvan mine, near Kryibo, Värmland, Sweden
- Bona de Padru, near Ozieri, Sardinia, Italy
- Higher Pitts Farm, Priddy, Somerset, England
- Kombat mine, 49 km south of Tsumeb, Namibia
Field-hunting tip
Where it forms: In a cavity in calcite in a metamorphosed stratiform zinc deposit (Franklin, New Jersey, USA); in veinlets cutting franklinite ore in bedded manganese deposits (Ushkatyn deposits, Kazakhstan). If you start seeing quartz, barite, apatite in float, you are in the right ground. Typical habit: crystalline, prismatic, wheat sheaf. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify kentrolite?+
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Is kentrolite safe to handle?+
What rocks look like kentrolite?+
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Find kentrolite on the map
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