The facts
What perthite actually is
Perthite is classified as feldspar intergrowth, with the composition KAlSi₃O₈ intergrown with NaAlSi₃O₈. It crystallises in the monoclinic host with triclinic lamellae system.
Colour comes from body colour from iron staining; the orange-gold schiller is interference from exsolution lamellae, which is also what a laboratory looks at when it is asked whether a colour is natural.
Refractive index 1.518–1.539. Specific gravity around 2.55–2.62. Cleavage: perfect basal and good prismatic. Those three numbers separate it from most of what imitates it.
Where perthite comes from
Perthite is produced at Perth, Ontario, Canada, Casa Ventura pegmatite, Goromonzi, Zimbabwe and Ambatondrazaka, Madagascar.
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 perthite is treated
Untreated ornamental feldspar. The name is textural rather than a species, so trade use is loose.
Treatment changes value, sometimes by a multiple, so it belongs in the description before the price and not after the sale.
What perthite is confused with
In the trade perthite is most often mistaken for, or substituted by, Labradorite, Sunstone or Moonstone.
The separation is rarely a matter of opinion: refractive index 1.518–1.539 and specific gravity 2.55–2.62 settle most of it in a minute, and magnification settles the rest.
What perthite is used for
Demand for perthite comes from jewellery, architecture and interiors, decorative objects and 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 carat, by the square metre or by the piece.
Durability and care
Hardness 6–6.5; cleavage perfect basal and good prismatic. That combination decides what it can safely be set into.
Hardness is not the whole story. Perfect cleavage means the stone can split cleanly if struck along the wrong plane, whatever its Mohs number, so a protective setting matters more here than the hardness suggests.
Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.
What perthite costs
As a guide, perthite trades around Slabs 2–15 USD/kg; cabochons 5–40 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 perthite treated, and how?
Untreated ornamental feldspar. The name is textural rather than a species, so trade use is loose.
Where does perthite come from?
Perth, Ontario, Canada, Casa Ventura pegmatite, Goromonzi, Zimbabwe and Ambatondrazaka, Madagascar. Origin affects price, so we name the locality rather than the country on every quote.
Is perthite hard enough to wear every day?
With care. It is 6–6.5 on the Mohs scale, which is hard enough, but perfect basal and good prismatic cleavage means it can split if struck at the wrong angle. Use a protective setting and avoid ultrasonic cleaning.
How much does perthite cost?
Indicatively Slabs 2–15 USD/kg; cabochons 5–40 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 perthite confused with?
Most often Labradorite, Sunstone and Moonstone. A refractive index of 1.518–1.539 and a specific gravity near 2.55–2.62 separate it quickly.
What is perthite used for besides jewellery?
architecture and interiors, decorative objects and mineral collecting. Each of those trades buys it in a different form and a different unit.
Related stones
Looking for perthite?
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 perthite