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, 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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