The facts
What jacobsite actually is
Mineralogically, jacobsite is spinel group — Mn²⁺Fe³⁺₂O₄, crystallising in the isometric system.
The colour is caused by opaque black from Mn–Fe charge transfer; brown internal reflections. 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 4.76–5.03; cleavage is none; uneven fracture.
Where jacobsite comes from
The recognised sources are Jakobsberg, Värmland, Sweden, Kalahari Manganese Field, Northern Cape, South Africa and Långban, Värmland, Sweden.
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 jacobsite is treated
Untreated. Weakly magnetic, which helps separate it from magnetite only with care. A specimen mineral.
None of this is a problem when it is said out loud. It becomes one the moment it is left out.
What jacobsite is confused with
The usual confusions are Magnetite, Franklinite and Hausmannite.
Because the material is opaque, refractive index is no help. Specific gravity around 4.76–5.03, hardness of 5.5–6.5, streak and magnification do the work instead.
What jacobsite is used for
Jacobsite 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
Jacobsite is 5.5–6.5 on the Mohs scale, with none; uneven fracture cleavage.
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 jacobsite costs
Indicative pricing for jacobsite is Specimens 15–150 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 jacobsite treated, and how?
Untreated. Weakly magnetic, which helps separate it from magnetite only with care. A specimen mineral.
Where does jacobsite come from?
Jakobsberg, Värmland, Sweden, Kalahari Manganese Field, Northern Cape, South Africa and Långban, Värmland, Sweden. Origin affects price, so we name the locality rather than the country on every quote.
Is jacobsite hard enough to wear every day?
Yes. At 5.5–6.5 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 jacobsite cost?
Indicatively Specimens 15–150 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 jacobsite confused with?
Most often Magnetite, Franklinite and Hausmannite. Since the material is opaque, separation relies on specific gravity near 4.76–5.03, hardness and magnification.
Related stones
Looking for jacobsite?
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 jacobsite