Banded purple and cream fluorite from one hill in Derbyshire. Effectively a finished resource.
China, Mexico, England (Weardale and Castleton), Illinois, Namibia
Blue John is a banded blue-purple and cream fluorite found in only one place on earth: Treak Cliff and the caverns beneath it at Castleton in Derbyshire. It was worked heavily through the eighteenth and nineteenth centuries for vases, urns, obelisks and inlay, and the workable reserves are now very nearly exhausted — extraction is limited to a few hundred kilograms a year at most, from a protected site.
That scarcity makes it the one fluorite with a genuine antiques market, and it also makes it worth identifying carefully. Genuine Blue John's banding is irregular, with the purple in wavering layers of varying width against cream and white, and it very often shows fine internal fractures because the material is naturally fissile — historically it had to be stabilised with resin or oil before it could be turned on a lathe, which is why antique pieces are impregnated as a matter of course.
Imitations are usually other banded fluorite, dyed or otherwise, or resin. The mineral tests apply unchanged: hardness 4, octahedral cleavage, UV fluorescence. What they cannot tell you is the locality, and locality is the whole value here — which makes provenance, and for antique pieces the form and workmanship, the real evidence.
These apply to this model and not to the rest of Fluorite. Work them alongside the maker's general checks, not instead of them.
Hardness 4, flat triangular cleavage and UV fluorescence establish that it is fluorite. Nothing physical establishes that it is Derbyshire fluorite, so the value question is a provenance question — documented history for antique pieces, and a named Castleton source for modern ones.
Blue John is naturally fissured and had to be stabilised with resin or oil to be turned. An antique piece showing no sign of impregnation at all is unusual, and a modern piece may be stabilised too. This is normal practice rather than a fault.
Genuine Blue John's purple bands waver, vary in width and fade irregularly into cream. Regular, evenly spaced, uniformly saturated banding suggests dyed material or a composite.
High for fluorite. Antique Blue John vases and bowls reach four and five figures; small modern turned pieces run tens to low hundreds.
An orientation for honest, unrestored condition — never an appraisal, and never a quotation.
Lovenhall StoneThe tests tell you what it is. The instrument reads a photograph and offers a name to start from — then hands you back to the tile and the coin, which are what settle it.