Rainbow Fluorite is just bands of different colours. Photo by Joanne Dusatko

Forget rubies, garnets and sapphires. Fluorite may be the world's most colourful mineral, because of the enormous range of brilliant and even iridescent colours it displays.

The funny thing is, pure fluorite crystals are transparent.

Fluorite is the mineral form of calcium fluoride,CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon.

Fluorite is Allochromatic, meaning that it can be tinted with elemental impurities. It is one of the most varied colored minerals in the mineral kingdom, and the colors may be very intense and almost electric.

A crystal's colour is dictated by the way light interacts with the chemicals in it, and by how these are bonded in an orderly structure, or lattice. Any impurities that work their way into fluorite's lattice can alter its apparent colour. For example, manganese ions turn it orange.

Structural defects within the lattice, known as colour centres, have a similar effect.

Fluorite comes in a wide range of colors and has consequently been dubbed "The most colorful mineral in the world". Every color of the rainbow in various shades are represented by fluorite samples, along with white, black, and clear crystals. Pure Fluorite is colorless; the color variations are caused by various various impurities.

The most common colors are purple, blue, green, yellow, or colorless. Less common are pink, red, white, brown, and black. Color zoning or banding is commonly present. The color of the fluorite is determined by factors including impurities, exposure to radiation, and the absence or voids of the color centers.

Fluorite's hallmark deep purple hue is the result of a small number of fluoride ions being permanently forced out of their lattice positions by irradiation or heating. When they move, an electron is left behind in each hole. When light hits the crystal, it is absorbed and re-emitted by these electrons, producing the colour we see.
Diagram to show the variation of crystal morphology at Nabburg-Wölsendorf as a function of temperature.  Three lines of evolution have been established based on the observation of the fl uorite mineralization at Nabburg-Wölsendorf. They were interpreted in terms of varying temperature gradients and correlated with temperatures published by ZIDAROVA et al. (1978) for similar fluorite habits.

Some fluorite specimens even have bands of different colours.

Fluorite forms in hydrothermal veins in the Earth's crust and in cavities in sedimentary rocks. Over the centuries, these fissures are constantly opening and closing, sometimes cutting off the fluids needed for fluorite to form. It's the subtle changes in the chemistry of these fluids that causes colour zoning in the crystals as they grow.

Some colors are deeply colored, and are especially pretty in large well-formed crystals, which Fluorite often forms. Sometimes coloring is caused by hydrocarbons, which can be removed from a specimen by heating. Some dealers may apply oil treatment upon amateur Fluorite specimens to enhance luster.

Rainbow Fluorite. photo: Joe Kienle

Fantastic fluorite on dolomite from Elmwood Mine, Tennessee. Credit: Anton Watzl

Stunning Fluorite crystal is from a southern Illinois mine. Matthew Webb @MineralSpecimen
Splendid fluorite crystals with a quartz on them.

Marvelous Fluorite from Shangbao Mine Hunan Province China.
Credit:  Exceptionalminerals..com
Beautiful sharp edged and intense yellow-colored fluorite from Aouli, Morocco. Photo © Egil Hollund
A perfect fluorite ball. The fluorite is not treated with oil or water. Collection, photo & © Egil Hollund

Amber coloured fluorite on quartz from Annaberg-Frohnau, Erzgebirge, Saxonia, Eastern Germany. Photo": © Jesse Fisher
Rare fluorite-slice from Wölsendorf, Bavaria! Collection, photo & © Gerhard Brandstetter
Fluorite and barite. from Guxian, Landkreis Tongbai, Provinz Henan Photo & © Joaquim Callen

Fluorite type second generation, a combination of the crystal forms of cube and rhombic dodecahedron. Collection, photo & © Andreas Schmid
Colour intense octahedron fluorite from Riemvasmaak fluorite occurrences, Kakamas District, Northern Cape Province, South Africa.Collection, photo & © Albert Russ

A botryoidal Fluorite from Gunxian cut and polished!  from Banded fluorite from Guxian, Xinyang Präfektur, Henan, China. Specimen, Photo & © Roland Noack
Remarkable Polished Rainbow Fluorite from Hunan Province, Hunan Province, China

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