Hardystonite is highly sought after by fluorescent mineral collectors due to its characteristic deep violet-blue glow under shortwave ultraviolet light. It occurs almost exclusively in the famous zinc-manganese orebodies of Franklin and Sterling Hill, New Jersey, typically as massive or granular grains within marble.
Is this hardystonite?
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 hardystonite with a known reference. Hardystonite 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. Hardystonite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Hardystonite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, gray, pink, colorless.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: granular to massive.
Often confused with
Hardystonite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside hardystonite
Minerals reported to co-occur with hardystonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂ZnSi₂O₇
- Mohs hardness
- 3
- Density
- 2.98 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Tetragonal
- Crystal habit
- Granular to Massive
- Cleavage
- Distinct
- Fluorescence
- Bright Violet-blue Under SW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphosed Zinc Ore Deposits
- Typical price
- $20-150 thumbnail to cabinet specimen
Where rockhounds find hardystonite
Classic worldwide localities
- Franklin, New Jersey, USA
- Sterling Hill, New Jersey, USA
Field-hunting tip
Look in metamorphosed zinc ore deposits country — that is the host setting where hardystonite typically forms. If you start seeing willemite, franklinite, calcite in float, you are in the right ground. Field specimens usually show a granular to massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find hardystonite on the map
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