The facts
What willemite actually is
The species behind willemite is willemite, Zn₂SiO₄; it forms in the trigonal system.
Yellow-green from Mn²⁺ in tetrahedral coordination; the same Mn²⁺ produces the famous intense green short-wave UV fluorescence is responsible for the colour — and the chromophore, not the name, is what decides whether a colour is stable.
On the instruments it reads a refractive index of 1.687–1.725 and a specific gravity of about 3.89–4.18, with poor to distinct — sources disagree cleavage.
Where willemite comes from
Commercial material comes from Franklin and Sterling Hill, Sussex County, New Jersey, USA, Tsumeb, Namibia and Mont Saint-Hilaire, Quebec, Canada.
Different localities give different colour and different clarity, and the trade prices them differently. We state which one.
How willemite is treated
Untreated. Bought overwhelmingly for its fluorescence — the Franklin assemblage of willemite, calcite and franklinite is the best-known fluorescent mineral suite in the world, and some specimens phosphoresce. Facetable transparent material from Tsumeb is scarce.
We state the treatment on every stone, including when the honest answer is that it cannot be determined. A treatment disclosed is a fact; a treatment discovered later is a refund.
What willemite is confused with
Watch for Peridot, Apatite, Sphalerite and Fluorescent calcite — these are what turn up sold under this name.
The separation is rarely a matter of opinion: refractive index 1.687–1.725 and specific gravity 3.89–4.18 settle most of it in a minute, and magnification settles the rest.
What willemite is used for
The trades that buy willemite are mineral collecting, decorative objects and jewellery. They do not want the same thing, and they do not pay in the same unit.
We quote each application in the unit that trade actually buys in, by the specimen, by the piece or by the carat.
Durability and care
Willemite is 5.5 on the Mohs scale, with poor to distinct — sources disagree cleavage.
With no cleavage plane to worry about, the practical limit is abrasion rather than breakage, and it takes daily wear well.
Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.
What willemite costs
Expect roughly Specimen pricing; faceted Tsumeb material $100–600/ct, depending on quality.
That is a range, not a quote. Colour, size, clarity, cut and origin move the figure a long way inside it, and the only honest price is one given against a specific stone. Send us what you need and we will price it.
Questions
Is willemite treated, and how?
Untreated. Bought overwhelmingly for its fluorescence — the Franklin assemblage of willemite, calcite and franklinite is the best-known fluorescent mineral suite in the world, and some specimens phosphoresce. Facetable transparent material from Tsumeb is scarce.
Where does willemite come from?
Franklin and Sterling Hill, Sussex County, New Jersey, USA, Tsumeb, Namibia and Mont Saint-Hilaire, Quebec, Canada. Origin affects price, so we name the locality rather than the country on every quote.
Is willemite hard enough to wear every day?
Yes. At 5.5 on the Mohs scale with no cleavage plane, it handles daily wear well. The practical limit is gradual abrasion rather than chipping.
How much does willemite cost?
Indicatively Specimen pricing; faceted Tsumeb material $100–600/ct. Colour, size, clarity and origin move the price a long way within that, so treat it as a range and ask for a quote against a specific stone.
What is willemite confused with?
Most often Peridot, Apatite, Sphalerite and Fluorescent calcite. A refractive index of 1.687–1.725 and a specific gravity near 3.89–4.18 separate it quickly.
What is willemite used for besides jewellery?
mineral collecting and decorative objects. Each of those trades buys it in a different form and a different unit.
Related stones
Looking for willemite?
Tell us the size, the quality and what it is for. We source it, photograph it and quote it — with the locality named.
Ask about willemite