The facts
What thomsonite actually is
The species behind thomsonite is thomsonite-Ca (zeolite group), NaCa₂Al₅Si₅O₂₀·6H₂O; it forms in the orthorhombic system.
Concentric 'eye' banding from radiating fibrous zoning with iron and copper oxide pigment; the chromophore is not documented in the gem literature 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 1.510–1.545 and a specific gravity of about 2.25–2.40, with perfect in one direction — sources disagree on the index cleavage.
Where thomsonite comes from
Commercial material comes from Grand Marais and the Lake Superior north shore, Minnesota, USA, Isle Royale, Michigan, USA, Kilpatrick Hills, Dunbartonshire, Scotland (type locality) and Jalgaon, Maharashtra, India.
Different localities give different colour and different clarity, and the trade prices them differently. We state which one.
How thomsonite is treated
Untreated. The banded 'eye' pebbles from the Lake Superior shore are the only form with a real ornamental market, and collecting is restricted in parts of that area.
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 thomsonite is confused with
Watch for Chlorastrolite, Agate, Prehnite and Serpentine — these are what turn up sold under this name.
The separation is rarely a matter of opinion: refractive index 1.510–1.545 and specific gravity 2.25–2.40 settle most of it in a minute, and magnification settles the rest.
What thomsonite is used for
The trades that buy thomsonite are jewellery, mineral collecting and decorative objects. 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 carat, by the specimen or by the piece.
Durability and care
Thomsonite is 5–5.5 on the Mohs scale, with perfect in one direction — sources disagree on the index 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 thomsonite costs
Expect roughly $2–40/ct for well-patterned eye material, 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 thomsonite treated, and how?
Untreated. The banded 'eye' pebbles from the Lake Superior shore are the only form with a real ornamental market, and collecting is restricted in parts of that area.
Where does thomsonite come from?
Grand Marais and the Lake Superior north shore, Minnesota, USA, Isle Royale, Michigan, USA, Kilpatrick Hills, Dunbartonshire, Scotland (type locality) and Jalgaon, Maharashtra, India. Origin affects price, so we name the locality rather than the country on every quote.
Is thomsonite hard enough to wear every day?
Not really. At 5–5.5 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 thomsonite cost?
Indicatively $2–40/ct for well-patterned eye material. 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 thomsonite confused with?
Most often Chlorastrolite, Agate, Prehnite and Serpentine. A refractive index of 1.510–1.545 and a specific gravity near 2.25–2.40 separate it quickly.
What is thomsonite 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 thomsonite?
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 thomsonite