Nasonite is a rare lead-calcium silicate mineral primarily known from the unique metamorphic deposits of Franklin, New Jersey. It is most easily identified by its distinct, bright blue fluorescence under longwave ultraviolet light, often appearing in massive or granular form associated with other fluorescent minerals like willemite.
Is this nasonite?
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 nasonite with a known reference. Nasonite sits at Mohs 4, 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: greasy to adamantine.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: cleaveable, massive.
Often confused with
Nasonite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads greasy to adamantine on Nasonite and vitreous on Hardystonite.
How to tell apart: Willemite is the harder of the two (Mohs 5.5 vs. 4); luster reads greasy to adamantine on Nasonite and vitreous to resinous on Willemite.
How to tell apart: Clinohedrite is the harder of the two (Mohs 5.5 vs. 4); luster reads greasy to adamantine on Nasonite and brilliant, glassy; pearly on {010} on Clinohedrite.
Often found alongside nasonite
Minerals reported to co-occur with nasonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₄Pb₆(Si₂O₇)₃Cl₂
- Mohs hardness
- 4
- Density
- 5.42-5.55 g/cm³
- Colors
- Streak
- White
- Luster
- Greasy to adamantine
- Transparency
- Transparent to translucent
- Crystal system
- Hexagonal
- Crystal habit
- Cleaveable, massive
- Cleavage
- Good on {0001}; indistinct prismatic
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare mineral, formed under hydrothermal conditions, cutting franklinite-willemite ore in a metamorphosed stratiform zinc deposit (Franklin, New Jersey, USA)
Where rockhounds find nasonite
Classic worldwide localities
- Franklin, Sussex Co., New Jersey, and at Crestmore, Riverside Co., California, USA
- Långban and Jakobsberg, Värmland, Sweden
Field-hunting tip
Where it forms: A rare mineral, formed under hydrothermal conditions, cutting franklinite-willemite ore in a metamorphosed stratiform zinc deposit (Franklin, New Jersey, USA). If you start seeing clinohedrite, barysilite, datolite in float, you are in the right ground. Typical habit: cleaveable, massive. Train your eye for that shape before scanning the outcrop.
Common questions
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Find nasonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
