The facts
What chlorastrolite actually is
The species behind chlorastrolite is pumpellyite, Ca₂(Mg,Fe)Al₂(SiO₄)(Si₂O₇)(OH)₂·H₂O; it forms in the monoclinic (radiating fibrous aggregate) system.
Fe²⁺–Fe³⁺ intervalence charge transfer with Fe²⁺; the turtleback or tortoiseshell pattern is radiating fibrous segment structure, not a colour effect 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 1.670–1.720 and a specific gravity of about 3.10–3.50, with none in the compact aggregate cleavage.
Where chlorastrolite comes from
Commercial material comes from Isle Royale, Michigan, USA and Keweenaw Peninsula, Michigan, USA.
Different localities give different colour and different clarity, and the trade prices them differently. We state which one.
How chlorastrolite is treated
Untreated. The state gem of Michigan. Collecting on Isle Royale National Park is now prohibited, so supply is old stock and Keweenaw beach material, which keeps prices firm for well-patterned pieces.
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 chlorastrolite is confused with
Watch for Thomsonite, Nephrite, Serpentine, Variscite and Turquoise — these are what turn up sold under this name.
The separation is rarely a matter of opinion: refractive index 1.670–1.720 and specific gravity 3.10–3.50 settle most of it in a minute, and magnification settles the rest.
What chlorastrolite is used for
The trades that buy chlorastrolite 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
Hardness 5–6; cleavage none in the compact aggregate. 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 chlorastrolite costs
Expect roughly $10–150/ct for sharply patterned 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 chlorastrolite treated, and how?
Untreated. The state gem of Michigan. Collecting on Isle Royale National Park is now prohibited, so supply is old stock and Keweenaw beach material, which keeps prices firm for well-patterned pieces.
Where does chlorastrolite come from?
Isle Royale, Michigan, USA and Keweenaw Peninsula, Michigan, USA. Origin affects price, so we name the locality rather than the country on every quote.
Is chlorastrolite hard enough to wear every day?
Not really. At 5–6 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 chlorastrolite cost?
Indicatively $10–150/ct for sharply patterned 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 chlorastrolite confused with?
Most often Thomsonite, Nephrite, Serpentine, Variscite and Turquoise. A refractive index of 1.670–1.720 and a specific gravity near 3.10–3.50 separate it quickly.
What is chlorastrolite 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 chlorastrolite?
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 chlorastrolite