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 3-3.5, 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: silky, dull, earthy.
- 4Match the color rangeCompare against the expected color range: white, pink, straw yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous.
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 5.5 vs. 3-3.5); streak differs, so Sussexite leaves white, Winchite leaves pale bluish gray; luster reads silky, dull, earthy on Sussexite and vitreous on Winchite.
How to tell apart: Tremolite is the harder of the two (Mohs 5-6 vs. 3-3.5); luster reads silky, dull, earthy 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
- MnBO₂(OH)
- Mohs hardness
- 3-3.5
- Density
- 3.30 g/cm³
- Colors
- Streak
- White
- Luster
- Silky, dull, earthy
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous
- Cleavage
- Good in one direction
- Rarity
- Rare
- Uses
- Collector, Research
- Host rock
- A rare hydrothermal mineral typically in veinlets in boron-bearing metamorphosed Mn–Fe–Zn deposits
Where rockhounds find sussexite
Classic worldwide localities
- Franklin and Sterling Hill, Ogdensburg, Sussex Co., New Jersey, USA
- Chicagon and Bengal mines, Iron Co., Michigan, USA
- Mountain Lake mine, Big Cottonwood district, Salt Lake Co., Utah, USA
- N’chwaning II and Hotazel mines, near Kuruman, Cape Province, South Africa
- Gonzen iron–manganese mine, near Sargans, St. Gallen Canton, Switzerland
- Kurihara mine, Mie Prefecture, the Yaei mine, Shiga Prefecture, the Hokkoji mine, Tochigi Prefecture, the Matsuo mine, Kochi Prefecture, and a number of other localities in Japan
Field-hunting tip
Where it forms: A rare hydrothermal mineral typically in veinlets in boron-bearing metamorphosed Mn–Fe–Zn deposits. If you start seeing pyrochroite, rhodochrosite, wiserite in float, you are in the right ground. Typical habit: fibrous. 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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