The facts
What williamsite actually is
The species behind williamsite is antigorite (serpentine group), Mg₃Si₂O₅(OH)₄; it forms in the monoclinic (aggregate) system.
Fe and Ni giving a deep oily green; black inclusions are chromite 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 1.560–1.571 (spot ~1.56) and a specific gravity of about 2.55–2.62, with not seen in the aggregate cleavage.
Where williamsite comes from
Commercial material comes from Rock Springs and the Cedar Hill Quarry, Lancaster County, Pennsylvania, USA and Harford County, Maryland, USA.
Different localities give different colour and different clarity, and the trade prices them differently. We state which one.
How williamsite is treated
Untreated. A translucent oil-green antigorite with characteristic chromite specks, historically cut as a jade substitute in the eastern United States; too soft for rings.
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 williamsite is confused with
Watch for Nephrite, Jadeite, Bowenite, Chrysoprase and Moss agate — these are what turn up sold under this name.
The separation is rarely a matter of opinion: refractive index 1.560–1.571 (spot ~1.56) and specific gravity 2.55–2.62 settle most of it in a minute, and magnification settles the rest.
What williamsite is used for
The trades that buy williamsite are carving and sculpture, decorative objects, mineral collecting 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 block, by the piece or by the specimen.
Durability and care
Williamsite is 3.5–4 on the Mohs scale, with not seen in the aggregate cleavage.
Below about 5.5 a stone will be scratched by ordinary household dust, which is largely quartz. That does not make it unusable — it makes it a pendant, an earring or an object rather than a ring worn every day.
Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.
What williamsite costs
Expect roughly $1–15/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 williamsite treated, and how?
Untreated. A translucent oil-green antigorite with characteristic chromite specks, historically cut as a jade substitute in the eastern United States; too soft for rings.
Where does williamsite come from?
Rock Springs and the Cedar Hill Quarry, Lancaster County, Pennsylvania, USA and Harford County, Maryland, USA. Origin affects price, so we name the locality rather than the country on every quote.
Is williamsite hard enough to wear every day?
Not really. At 3.5–4 on the Mohs scale it is softer than the quartz dust in ordinary household dirt, so it scratches with wear. It suits pendants, earrings and objects better than a daily ring.
How much does williamsite cost?
Indicatively $1–15/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 williamsite confused with?
Most often Nephrite, Jadeite, Bowenite, Chrysoprase and Moss agate. A refractive index of 1.560–1.571 (spot ~1.56) and a specific gravity near 2.55–2.62 separate it quickly.
What is williamsite used for besides jewellery?
carving and sculpture, decorative objects and mineral collecting. Each of those trades buys it in a different form and a different unit.
Related stones
Looking for williamsite?
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 williamsite