Fluorite, also called fluorspar, is a mineral composed of calcium fluoride, found in a wide range of colours including purple, blue, green, yellow and colourless, often banded or zoned within a single crystal. It is relatively soft and brittle, so carving and turning it demand considerable skill, but it can take a lovely polish and has long been used for decorative objects and mineral specimens.
The most famous decorative variety in Britain is Blue John, a banded purple, blue and yellow fluorite mined near Castleton in Derbyshire. Blue John was particularly fashionable in the later eighteenth century, when it was turned into urns, vases, candlesticks, obelisks and inlays, and Matthew Boulton famously mounted it in gilt bronze for wealthy clients. Fluorite from other sources was also carved in China and elsewhere into small ornaments. Because fluorite is fragile, old pieces are frequently stabilised with resin, a practice dating back centuries, and cracks or repairs are common. Collectors value depth and contrast of colour, good translucency, size and original mounts. Displayed in natural light, a fine Blue John urn or a vivid fluorite crystal has a remarkable glowing quality that suits both period and modern interiors.
