The facts
What proustite actually is
Proustite is classified as proustite, with the composition Ag₃AsS₃. It crystallises in the trigonal system.
Colour comes from ag–As–S charge transfer giving a deep scarlet transmitted colour; opaque and metallic-looking in reflected light, which is also what a laboratory looks at when it is asked whether a colour is natural.
Refractive index 2.79–3.08. Specific gravity around 5.57. Cleavage: distinct {1011}. Those three numbers separate it from most of what imitates it.
Where proustite comes from
Proustite is produced at Chañarcillo, Copiapó, Chile, Sankt Andreasberg, Harz, Germany, Jáchymov, Czech Republic and Imiter Mine, Morocco.
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 proustite is treated
Untreated but strongly light-sensitive: proustite darkens irreversibly from translucent ruby-red to dull black on light exposure, so historic Chañarcillo specimens are usually kept permanently boxed. Extremely fragile and never cut for wear.
Treatment changes value, sometimes by a multiple, so it belongs in the description before the price and not after the sale.
What proustite is confused with
In the trade proustite is most often mistaken for, or substituted by, Pyrargyrite, Cinnabar, Cuprite or Realgar.
The separation is rarely a matter of opinion: refractive index 2.79–3.08 and specific gravity 5.57 settle most of it in a minute, and magnification settles the rest.
What proustite is used for
Demand for proustite 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 2–2.5; cleavage distinct {1011}. 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 proustite costs
As a guide, proustite trades around Specimens $100–$20,000 for fine Chañarcillo or Harz crystals.
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 proustite treated, and how?
Untreated but strongly light-sensitive: proustite darkens irreversibly from translucent ruby-red to dull black on light exposure, so historic Chañarcillo specimens are usually kept permanently boxed. Extremely fragile and never cut for wear.
Where does proustite come from?
Chañarcillo, Copiapó, Chile, Sankt Andreasberg, Harz, Germany, Jáchymov, Czech Republic and Imiter Mine, Morocco. Origin affects price, so we name the locality rather than the country on every quote.
Is proustite hard enough to wear every day?
Not really. At 2–2.5 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 proustite cost?
Indicatively Specimens $100–$20,000 for fine Chañarcillo or Harz crystals. 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 proustite confused with?
Most often Pyrargyrite, Cinnabar, Cuprite and Realgar. A refractive index of 2.79–3.08 and a specific gravity near 5.57 separate it quickly.
Related stones
Looking for proustite?
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 proustite