Alleghanyite is a rare manganese silicate mineral typically found in metamorphosed ore deposits. It is most frequently encountered in massive or granular forms, often associated with other manganese minerals like spessartine and willemite.
Is this alleghanyite?
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 alleghanyite with a known reference. Alleghanyite sits at Mohs 5.5, 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: vitreous to dull.
- 4Match the color rangeCompare against the expected color range: white, brown, bright pink, grayish pink.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: granular, massive.
Often confused with
Alleghanyite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Gahnite is the harder of the two (Mohs 7.5-8 vs. 5.5); streak differs, so Alleghanyite leaves white, Gahnite leaves gray.
How to tell apart: Spessartine is the harder of the two (Mohs 7-7.5 vs. 5.5).
Often found alongside alleghanyite
Minerals reported to co-occur with alleghanyite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn₅(SiO₄)₂(OH)₂
- Mohs hardness
- 5.5
- Density
- 4.020 g/cm³
- Streak
- White
- Luster
- Vitreous to dull
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Granular, massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Research
- Host rock
- Hydrothermally deposited, in lenses in a manganese-bearing vein (Bald Knob, North Carolina, USA)
Where rockhounds find alleghanyite
Classic worldwide localities
- Bald Knob, near Sparta, Alleghany Co., North Carolina, USA
- Franklin and Sterling Hill, Ogdensburg, Sussex Co., New Jersey, USA
- Germolis prospect, Fiddleton, Amador Co., and at Alum Rock Park, Santa Clara Co., California, USA
- Eureka, Hinsdale Co., and the Sunnyside mine, San Juan Co., Colorado, USA
- Benallt mine, Rhiw, Lleyn Peninsula, Wales
- Långban, and in the Brattfors mine, Nordmark, Värmland, Sweden
Field-hunting tip
Where it forms: Hydrothermally deposited, in lenses in a manganese-bearing vein (Bald Knob, North Carolina, USA). If you start seeing spessartine, rhodonite, galaxite in float, you are in the right ground. Typical habit: granular, massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify alleghanyite?+
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What rocks look like alleghanyite?+
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Find alleghanyite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
