The facts
What marcasite actually is
Mineralogically, marcasite is marcasite — FeS₂, crystallising in the orthorhombic system.
The colour is caused by metallic conduction band; paler and greener than pyrite, tarnishing quickly. That is worth knowing because it determines what heating, light and time can and cannot do to the stone.
A refractometer gives nothing, because the material is opaque, and the specific gravity sits near 4.85–4.92; cleavage is distinct {101}.
Where marcasite comes from
The recognised sources are Folkestone and Dover, Kent, England (chalk nodules), Sparta, Randolph County, Illinois, USA and Cap Blanc-Nez, Pas-de-Calais, France.
Origin affects price in this material, so we name the locality on every quote rather than the country. "African" or "Asian" tells a buyer nothing.
How marcasite is treated
Untreated and inherently unstable: marcasite oxidises in humid air to sulphuric acid and iron sulphates, destroying itself and any labels or cabinet nearby. Because of this it is never used in jewellery — the trade's 'marcasite' is pyrite. Store with a desiccant.
None of this is a problem when it is said out loud. It becomes one the moment it is left out.
What marcasite is confused with
The usual confusions are Pyrite, Arsenopyrite, Chalcopyrite and Löllingite.
Because the material is opaque, refractive index is no help. Specific gravity around 4.85–4.92, hardness of 6–6.5, streak and magnification do the work instead.
What marcasite is used for
Marcasite is bought by mineral collecting — and each of those trades wants a different form of the same material.
We quote each application in the unit that trade actually buys in, by the specimen.
Durability and care
Hardness 6–6.5; cleavage distinct {101}. That combination decides what it can safely be set into.
With no cleavage plane to worry about, the practical limit is abrasion rather than breakage, and it takes daily wear well.
Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.
What marcasite costs
Indicative pricing for marcasite is Specimens $10–$300.
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 marcasite treated, and how?
Untreated and inherently unstable: marcasite oxidises in humid air to sulphuric acid and iron sulphates, destroying itself and any labels or cabinet nearby. Because of this it is never used in jewellery — the trade's 'marcasite' is pyrite. Store with a desiccant.
Where does marcasite come from?
Folkestone and Dover, Kent, England (chalk nodules), Sparta, Randolph County, Illinois, USA and Cap Blanc-Nez, Pas-de-Calais, France. Origin affects price, so we name the locality rather than the country on every quote.
Is marcasite hard enough to wear every day?
Yes. At 6–6.5 on the Mohs scale with no cleavage plane, it handles daily wear well. The practical limit is gradual abrasion rather than chipping.
How much does marcasite cost?
Indicatively Specimens $10–$300. 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 marcasite confused with?
Most often Pyrite, Arsenopyrite, Chalcopyrite and Löllingite. Since the material is opaque, separation relies on specific gravity near 4.85–4.92, hardness and magnification.
Related stones
Looking for marcasite?
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 marcasite