The facts
What sellaite actually is
The species behind sellaite is magnesium fluoride, MgF₂; it forms in the tetragonal system.
Colourless; among the lowest refractive indices of any faceted gem, below fluorite is responsible for the colour — and the chromophore, not the name, is what decides whether a colour is stable.
On the instruments it reads a refractive index of 1.378–1.390 and a specific gravity of about 3.14–3.16, with good prismatic cleavage.
Where sellaite comes from
Commercial material comes from Pedra Preta pit, Brumado, Bahia, Brazil, Gebel Meharu, Egypt and Stassfurt, Saxony-Anhalt, Germany.
Different localities give different colour and different clarity, and the trade prices them differently. We state which one.
How sellaite is treated
Untreated. Brumado magnesite deposits supply the only significant facetable crystals. Its synthetic equivalent is a standard infrared optical window material.
We state the treatment on every stone, including when the honest answer is that it cannot be determined. A treatment disclosed is a fact; a treatment discovered later is a refund.
What sellaite is confused with
Watch for Fluorite, Quartz, Danburite and Phenakite — these are what turn up sold under this name.
The separation is rarely a matter of opinion: refractive index 1.378–1.390 and specific gravity 3.14–3.16 settle most of it in a minute, and magnification settles the rest.
What sellaite is used for
The trades that buy sellaite are mineral collecting and technical and precision components. They do not want the same thing, and they do not pay in the same unit.
We quote each application in the unit that trade actually buys in, by the specimen or by the piece.
Durability and care
Hardness 5–5.5; cleavage good prismatic. 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 sellaite costs
Expect roughly Faceted stones 100–400 USD/ct, depending on quality.
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 sellaite treated, and how?
Untreated. Brumado magnesite deposits supply the only significant facetable crystals. Its synthetic equivalent is a standard infrared optical window material.
Where does sellaite come from?
Pedra Preta pit, Brumado, Bahia, Brazil, Gebel Meharu, Egypt and Stassfurt, Saxony-Anhalt, Germany. Origin affects price, so we name the locality rather than the country on every quote.
Is sellaite hard enough to wear every day?
Not really. At 5–5.5 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 sellaite cost?
Indicatively Faceted stones 100–400 USD/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 sellaite confused with?
Most often Fluorite, Quartz, Danburite and Phenakite. A refractive index of 1.378–1.390 and a specific gravity near 3.14–3.16 separate it quickly.
Related stones
Looking for sellaite?
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 sellaite