Willemite is world-renowned among collectors for its spectacular, brilliant green fluorescence under shortwave ultraviolet light. It is typically found in massive, granular, or prismatic forms, often intimately associated with franklinite and zincite in the unique deposits of New Jersey. Its name honors King William I of the Netherlands.
Is this willemite?
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 willemite with a known reference. Willemite 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. Willemite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Willemite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, green, yellow, brown, red.
- 5Look at form & habitCrystal system: trigonal. Typical habit: prismatic crystals, massive, granular.
Often confused with
Willemite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside willemite
Minerals reported to co-occur with willemite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Zn₂SiO₄
- Mohs hardness
- 5.5
- Density
- 3.9-4.2 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Prismatic Crystals, Massive, Granular
- Cleavage
- Good in One Direction
- Fluorescence
- Bright Green Under SW UV
- Rarity
- Uncommon
- Uses
- Collector, Fluorescent Mineral Display, Ore of Zinc
- Host rock
- Metamorphosed Zinc Ore Deposits
- Typical price
- $10-100 thumbnail, $50-500 cabinet specimen
Where rockhounds find willemite
5 mapped spotsClassic worldwide localities
- Franklin, New Jersey, USA
- Ogdensburg, New Jersey, USA
- Tsumeb, Namibia
- Broken Hill, Australia
Field-hunting tip
Look in metamorphosed zinc ore deposits country — that is the host setting where willemite typically forms. If you start seeing franklinite, zincite, calcite in float, you are in the right ground. Field specimens usually show a prismatic crystals, massive, granular habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in New Jersey, Arizona, New Mexico — start trip planning there.
Common questions
How do you identify willemite?+
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Can I find willemite in the United States?+
How much is willemite worth?+
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Find willemite on the map
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