The facts
What thaumasite actually is
Thaumasite is classified as calcium silicate-carbonate-sulphate, with the composition Ca₆Si₂(CO₃)₂(SO₄)₂(OH)₁₂·24H₂O. It crystallises in the hexagonal system.
Colour comes from colourless to white or pale yellow; no chromophore, which is also what a laboratory looks at when it is asked whether a colour is natural.
Refractive index 1.467–1.505. Specific gravity around 1.88–1.91. Cleavage: poor. Those three numbers separate it from most of what imitates it.
Where thaumasite comes from
Thaumasite is produced at N'Chwaning Mines, Northern Cape, South Africa, Wessels Mine, Northern Cape, South Africa and Paterson, New Jersey, USA.
The locality is part of the description, not a footnote — two stones of the same weight from two of these places are not the same stone.
How thaumasite is treated
Untreated. Notable outside gemmology as a destructive concrete-attack product. Faceted stones are soft rarities cut from Kalahari material.
Treatment changes value, sometimes by a multiple, so it belongs in the description before the price and not after the sale.
What thaumasite is confused with
In the trade thaumasite is most often mistaken for, or substituted by, Ettringite, Natrolite or Calcite.
The separation is rarely a matter of opinion: refractive index 1.467–1.505 and specific gravity 1.88–1.91 settle most of it in a minute, and magnification settles the rest.
What thaumasite is used for
Demand for thaumasite comes from mineral collecting, which is why one price per carat never covers it.
We quote each application in the unit that trade actually buys in, by the specimen.
Durability and care
Hardness 3.5; cleavage poor. That combination decides what it can safely be set into.
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 thaumasite costs
As a guide, thaumasite trades around Faceted stones 80–400 USD/ct; specimens 30–250 USD.
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 thaumasite treated, and how?
Untreated. Notable outside gemmology as a destructive concrete-attack product. Faceted stones are soft rarities cut from Kalahari material.
Where does thaumasite come from?
N'Chwaning Mines, Northern Cape, South Africa, Wessels Mine, Northern Cape, South Africa and Paterson, New Jersey, USA. Origin affects price, so we name the locality rather than the country on every quote.
Is thaumasite hard enough to wear every day?
Not really. At 3.5 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 thaumasite cost?
Indicatively Faceted stones 80–400 USD/ct; specimens 30–250 USD. 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 thaumasite confused with?
Most often Ettringite, Natrolite and Calcite. A refractive index of 1.467–1.505 and a specific gravity near 1.88–1.91 separate it quickly.
Related stones
Looking for thaumasite?
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 thaumasite