Fluorspar

What fluorspar actually is

Mineralogically, fluorspar is calcium fluoride, the sole significant commercial source of fluorine for the entire chemical industry — CaF2; acid-grade requires over 97% CaF2, metallurgical grade 60-85%, crystallising in the cubic system.

The colour is caused by colour centres from radiation damage and rare-earth substitution give purple, green, blue and yellow; it is the origin of the word fluorescence. That is worth knowing because it determines what heating, light and time can and cannot do to the stone.

A refractometer reads 1.433-1.435 - the lowest RI of any common mineral, which is why it is used for apochromatic lenses, and the specific gravity sits near 3.00-3.25; cleavage is perfect octahedral in four directions - which makes gem fluorite very fragile to wear.

Where fluorspar comes from

The recognised sources are Las Cuevas, San Luis Potosi, Mexico - the largest single fluorspar mine in the world, Inner Mongolia, Zhejiang and Hunan, China, Vergenoeg and Witkop, South Africa, Castleton, Derbyshire, England (Blue John, the banded ornamental variety, now a few kilograms a year) and Mongolia, Vietnam, Spain and Morocco.

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 fluorspar is treated

Flotation-concentrated; nothing else. Acid-grade goes to hydrofluoric acid, and from there to fluoropolymers, refrigerants, aluminium smelting, uranium processing and pharmaceuticals; metallurgical grade is a steel and cement flux; ceramic grade goes to opal glass and enamels. Fluorspar is on the EU, US and UK critical raw materials lists. BLUE JOHN is a separate matter: a uniquely banded purple-and-yellow fluorite from two small Derbyshire mines, where extraction is now a few kilograms annually under National Trust and Peak District controls - it is impregnated with resin to be workable at all, and most 'Blue John' sold is either antique, dyed fluorite from China, or resin. Gem fluorite is too soft and too cleavable for rings.

None of this is a problem when it is said out loud. It becomes one the moment it is left out.

What fluorspar is confused with

The usual confusions are Dyed Chinese fluorite sold as Blue John, Calcite and barite (the common gangue), Amethyst and glass for gem fluorite and Cryolite (the historic alternative fluorine source, now exhausted).

The separation is rarely a matter of opinion: refractive index 1.433-1.435 - the lowest RI of any common mineral, which is why it is used for apochromatic lenses and specific gravity 3.00-3.25 settle most of it in a minute, and magnification settles the rest.

What fluorspar is used for

Fluorspar is bought by heavy industry, carving and sculpture, mineral collecting, decorative objects and jewellery — 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 tonne, by the block or by the specimen.

Durability and care

Fluorspar is 4 - the Mohs 4 reference mineral on the Mohs scale, with perfect octahedral in four directions - which makes gem fluorite very fragile to wear cleavage.

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 fluorspar costs

Indicative pricing for fluorspar is $400-650 per tonne acid-grade; $250-400 per tonne metallurgical grade; genuine antique Blue John objects $500-20,000.

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.

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