Sussexite is a rare manganese borate typically found as fibrous, silky white to pale yellowish masses or radiating sprays. It is most famously associated with the unique mineral assemblages of the Franklin and Sterling Hill mining districts in New Jersey. Collectors should look for its distinctive fibrous habit occurring alongside fluorescent willemite or metallic franklinite.
Is this sussexite?
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 sussexite with a known reference. Sussexite sits at Mohs 3-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Sussexite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Sussexite typically shows a silky luster.
- 4Match the color rangeCompare against the expected color range: white, yellowish-white, pinkish-white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: fibrous, acicular, radiating, or massive.
Often confused with
Sussexite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Winchite is the harder of the two (Mohs 5-6 vs. 3-4); luster reads silky on Sussexite and vitreous on Winchite.
How to tell apart: Tremolite is the harder of the two (Mohs 5-6 vs. 3-4); luster reads silky on Sussexite and vitreous on Tremolite.
Often found alongside sussexite
Minerals reported to co-occur with sussexite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn²⁺₂B₂O₅(OH)₂
- Mohs hardness
- 3-4
- Density
- 3.12 g/cm³
- Streak
- White
- Luster
- Silky
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Fibrous, Acicular, Radiating, Or Massive
- Cleavage
- Good in One Direction
- Rarity
- Rare
- Uses
- Collector, Research
- Host rock
- Metamorphosed Zinc-manganese Ore Deposits
- Typical price
- $20-150 for small specimens
Where rockhounds find sussexite
Classic worldwide localities
- Franklin, New Jersey, USA
- Sterling Hill, New Jersey, USA
- Langban, Sweden
Field-hunting tip
Look in metamorphosed zinc-manganese ore deposits country — that is the host setting where sussexite typically forms. If you start seeing willemite, franklinite, zincite in float, you are in the right ground. Field specimens usually show a fibrous, acicular, radiating, or massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find sussexite on the map
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