The facts
What siderite actually is
Mineralogically, siderite is siderite — FeCO₃, crystallising in the trigonal system.
The colour is caused by fe²⁺ giving honey-yellow to amber-brown, darkening as it oxidises. That is worth knowing because it determines what heating, light and time can and cannot do to the stone.
A refractometer reads 1.633–1.873, and the specific gravity sits near 3.83–3.96; cleavage is perfect rhombohedral.
Where siderite comes from
The recognised sources are Panasqueira, Portugal, Ivigtut, Greenland, Morro Velho, Minas Gerais, Brazil and Cornwall (Wheal Maudlin), England.
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 siderite is treated
Untreated. Surfaces tarnish to brown iron oxide over time and specimens should be kept dry; faceted siderite is rare, soft and shows strong doubling.
None of this is a problem when it is said out loud. It becomes one the moment it is left out.
What siderite is confused with
The usual confusions are Sphalerite, Calcite, Dolomite and Smithsonite.
The separation is rarely a matter of opinion: refractive index 1.633–1.873 and specific gravity 3.83–3.96 settle most of it in a minute, and magnification settles the rest.
What siderite is used for
Siderite is bought by mineral collecting and metallurgy — 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 3.5–4.5; cleavage perfect rhombohedral. 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 siderite costs
Indicative pricing for siderite is Specimens $20–$1,500; faceted stones $40–$200/ct.
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 siderite treated, and how?
Untreated. Surfaces tarnish to brown iron oxide over time and specimens should be kept dry; faceted siderite is rare, soft and shows strong doubling.
Where does siderite come from?
Panasqueira, Portugal, Ivigtut, Greenland, Morro Velho, Minas Gerais, Brazil and Cornwall (Wheal Maudlin), England. Origin affects price, so we name the locality rather than the country on every quote.
Is siderite hard enough to wear every day?
Not really. At 3.5–4.5 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 siderite cost?
Indicatively Specimens $20–$1,500; faceted stones $40–$200/ct. 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 siderite confused with?
Most often Sphalerite, Calcite, Dolomite and Smithsonite. A refractive index of 1.633–1.873 and a specific gravity near 3.83–3.96 separate it quickly.
Related stones
Looking for siderite?
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 siderite