Fluorite

Fluorite (calcium fluoride) is often called "the most colourful mineral in the world". Pure fluorite is colourless, but traces of other elements and natural radiation give it a remarkable range of colours, including purple, blue, green, yellow, pink, brown and black. Many stones show bands or zones of several colours in a single piece, known as rainbow fluorite, which is very popular for beads and carvings.

The name comes from the Latin "fluere", meaning to flow, because fluorite was used as a flux to help metals melt in smelting. Fluorite also gave its name to fluorescence: many fluorite specimens glow, usually blue or violet, under ultraviolet light, and the phenomenon was first studied in fluorite in the 19th century. Fluorite is also an important industrial mineral, used to make hydrofluoric acid, steel, aluminium and optical lenses.

Fluorite forms distinctive cube- and octahedron-shaped crystals. It is soft (4 on the Mohs scale, the reference mineral for that level) and has perfect cleavage in four directions, so it can split easily. The most famous British fluorite is Blue John, a purple and yellow banded fluorite mined in Castleton, Derbyshire, since Roman times and carved into vases and ornaments. Other important sources include China, Mexico, South Africa, Spain, Germany, Argentina and the USA.

Fluorite is generally untreated but may be stabilised with resin or occasionally irradiated or heated to change its colour. Its colours are sometimes confused with amethyst, emerald or aquamarine, but fluorite is much softer.

Fluorite at a glance

Caring for fluorite

Fluorite is soft (4 on the Mohs scale) and has perfect cleavage in four directions, so it scratches, chips and splits easily. It is best for earrings, pendants and necklaces rather than rings or bracelets. Clean it gently with lukewarm soapy water and a soft cloth. Never use ultrasonic or steam cleaners, and avoid heat, sudden temperature changes and acids. Keep it out of strong sunlight for long periods, as some colours may fade. Store separately in a soft pouch.

In folklore

The beliefs below are traditional folklore, included for interest. They are not scientifically proven, and nothing here is medical advice.

In ancient China, fluorite was carved into ornaments and used as a protective charm, and the Romans are said to have carved it into drinking vessels in the belief that it would prevent drunkenness. Blue John has been treasured in England for centuries, and a legend says that Roman vases made from it were found at Pompeii. Fluorite is associated with the zodiac signs Pisces and Capricorn.

Fluorite is traditionally regarded as a stone of order, focus and mental clarity, sometimes called the "genius stone". Crystal healing lore holds that it improves concentration and decision-making, brings structure to chaotic thoughts and protects against negative energy. Each colour is given its own meaning: purple with intuition, green with renewal and blue with calm communication. It is linked to the heart, throat and third eye chakras.

Related stones

Rainbow fluorite, Blue John and yttrium fluorite. Stones that can look similar include amethyst, emerald, aquamarine, apatite, calcite, green tourmaline and glass. Fluorite is also used to imitate more valuable gems.

For the technically minded

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