A rare pink fluorite specimen with exceptional brightness. 18.56-ct, oval brilliant cut, Chumar Bakhoor, Hunza Valley, Gilgit District, Gilgit-Baltistan (Northern Areas), Pakistan. © Rob Lavinsky, www.iRocks.com. Cropped to show detail. Used with permission.
Although too fragile for most jewelry use, fluorites are often faceted for collectors. They occur in a wide range of attractive colors and can be extremely bright. These gems are also renowned for their fluorescence.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
| Data | Value |
|---|---|
| Name | Fluorite |
| Varieties | Blue John |
| Crystallography | Isometric. Usually in good crystals, cubes, octahedra, and other forms, often twinned; also massive, granular. |
| Crystallographic Forms | |
| Refractive Index | 1.432-1.434 |
| Colors | An extremely wide range is represented: colorless, purple (various shades), green (various shades), blue-green, blue, yellow to orange, brown (various shades), white, pink, red, brownish red, pinkish red, brownish black, black. Crystals are frequently color zoned. |
| Luster | Vitreous |
| Hardness | 4 |
| Fracture | Subconchoidal, splintery. |
| Specific Gravity | 3.180; massive material with impurities 3.0-3.25. |
| Birefringence | None |
| Cleavage | Perfect 4 directions. Cleavage is octahedral, very easy. |
| Dispersion | 0.007 (very low) |
| Luminescence | See "Fluorite Properties" below. |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, Phosphorescent, UV-Long, X-ray Colors |
| Enhancements | Faceted gems may receive heat treatment or irradiation. Decorative objects may receive coating, dyeing, and plastic impregnation. |
| Typical Treatments | Dyeing, Heat Treatment, Infusion/Impregnation, Irradiation, Surface Coating |
| Transparency | Opaque to transparent |
| Absorption Spectrum | U and rare earths are often present; spectrum reflects their presence. Spectra usually vague, however. Green material has lines at 6340, 6100, 5820, and 4450 and a broad band at 4270. |
| Phenomena | Color change (Very rare) |
| Formula | CaF2 |
| Pleochroism | None |
| Optics | Isotropic; N = 1.432-1.434. |
| Etymology | From the Latin fluere, “to flow,” because it melts easily and is used as a flux in smelting. |
| Occurrence | In hydrothermal deposits; sedimentary rocks; hot springs; rarely in pegmatites; usually associated with sulfide ore deposits. |
| Inclusions | Mineral crystals, cavities (single, two, and/or three phase), healed fractures. |
Fluorite: Canada (6.14), Illinois (17.1) // Germany (4.35), Colombia (13.0), New Mexico (1.2), Switzerland (3.5). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Despite its low refractive index (RI), fluorite can take a high polish. This means faceted fluorites can show exceptional brilliance. Many fluorite crystals are also transparent.
Fluorites come in many colors, including colorless. Most available stones occur in shades of purple, blue, or green. Chrome green material from Colombia and pink gems are rare. Lapidaries can cut multi-colored gems (sometimes called “rainbow fluorites”) from color zoned crystals, too.
Atomic-age inspired sterling silver pendant with a rainbow fluorite stone. Photo by Rhonda. Licensed under CC By-SA 2.0.
Chemical impurities and natural irradiation contribute to fluorite’s colorful varieties. Very rarely, some fluorites display a color change effect, from blue in daylight to purple or lavender in incandescent light. (Materials from England and Cherbadung, Switzerland have demonstrated this).
Fluorite: Colombia (3.05), Switzerland (0.92), Illinois (15.20) // Illinois (5.75), England (6.05), Illinois (8.80). Photo © Joel E. Arem, PhD, FGA. Used with permission.
For over 1,500 years, English artisans used Blue John or Derbyshire Spar as decorative material in vases, carvings, bowls, and so forth. This fluorite variety has bands of white, blue, violet, and reddish brown.
Candelabra with Blue John, circa 1860. Photo by Rauantiques. Licensed under CC By-SA 4.0.
The Derbyshire deposits are nearly exhausted. However, a similar type of fluorite has been discovered in China.
A craftsman at the Treak Cliff Cavern workshop in Derbyshire, England placed slices of Blue John, too thin for jewelry, on his window. Photo by Andy Mabbett. Licensed under CC By-SA 3.0. (Cropped to show detail).
Some (but not all) fluorites display fluorescence under ultraviolet light (UV). Thus, confirming the presence of this property isn’t diagnostic for identifying fluorite. However, this property is strongly associated with this gem. In fact, in 1852, the physicist Sir George Gabriel Stokes named this effect “fluorescence” after his studies of the mineral fluorite.
Green fluorite crystal under normal light (left) and UV light (right). Photo by GorissM. Licensed under CC By-SA 2.0.
The presence of uranium (U) and rare-earth elements likely cause fluorite’s fluorescence. However, sometimes organic inclusions (hydrocarbons) may be the cause.
Under longwave UV, fluorites can fluoresce yellow, blue, white, reddish, violet, or green.
Some fluorites exhibit phosphorescence under X-rays, a luminescence that lasts even after the light source is removed. Some material is also thermoluminescent, luminescing when heated.
Fluorescent fluorites with a coating of quartz crystals, Allenheads Mine, East Allendale, North Pennines, Northumberland, England, UK. © Rob Lavinsky, www.iRocks.com. Used with permission.
Chlorophane, a rare fluorite variety, shows phosphorescence and thermoluminescence, as well as triboluminescence. It luminesces when rubbed or held in your hand.
Chlorophane under normal light (left) and UV shortwave light (right), Buckwheat dump mineral collecting site, Franklin, Franklin Mining District, Sussex Co., New Jersey, USA. Photo by Modris Baum. Public domain.
Lab-created fluorite in all its various colors is available. The optics industry especially values fluorite for the creation of high-quality lenses. Its low RI and low dispersion make it an ideal lens material. Not surprisingly, the search for cheaper synthetic production continues apace. Some manufacturers melt and mix high-purity natural fluorites with other materials to create high-quality lenses.
Currently, high production costs, combined with fluorite’s low hardness and perfect cleavage, make synthetics an improbable choice for jewelry.
Due to their considerable color range, you’ll more likely find natural fluorites misidentified or misrepresented as other gems. For example, fluorites have been offered as amethysts, emeralds, and color change garnets.
Hardness testing, of course, is the easiest way to distinguish fluorites from these more popular and durable jewelry stones. However, conduct scratch testing only as a last resort and never on a finished gem. Fortunately, fluorite’s very low RI and dispersion can help distinguish it from many other gems.
One of the more unusual examples of fluorite as a simulant has appeared in Asian markets. So-called “night glowing pearls” aren’t pearls at all but often spherical fluorites, sometimes untreated but sometimes coated with a material to enhance phosphorescence.
Heating to 100-150° C can lighten dark-colored fluorites, but higher temperatures risk removing all color. On the other hand, radiation treatment can turn colorless and pale green material darker blue, green, or purple.
Decorative objects might receive coating, dyeing, and plastic impregnation treatments.
Fluorites occur in many localities worldwide.
Fluorite: Africa (62.55), New Hampshire (152.90), Illinois (17.55), New Hampshire (38.10). Photo © Joel E. Arem, PhD, FGA. Used with permission.
The most well-known sources of gem-quality material include the following:
Faceted fluorite, Argentina. Photo by Didier Descouens. Licensed under CC By-SA 3.0.
Since suitable rough from a wide range of localities is available, fluorite crystals can be very large. However, large stones totally free of internal flaws are extremely rare. Thus, cut fluorites suitable for jewelry use are usually small.
Fluorite: Illinois (1,031 cts, world’s largest of this color). Photo © Joel E. Arem, PhD, FGA. Used with permission.
One of the largest known fluorite gems, 3,965.35 cts, on display at the Smithsonian National Museum of Natural History in Washington, DC. Photo by thisisbossi. Licensed under CC By-SA 2.0.
Fluorites contain fluorine (F) as part of their chemical makeup (CaF2). As a gas, fluorine is very toxic. However, fluorites are inert. Wearing or holding fluorite gems or jewelry will pose no health risks. The lapidary processes used to cut fluorites won’t create fluorine gas. (Of course, gem cutters should take basic precautions when working with any gem material).
There are health risks associated with long-term exposure to massive amounts of fluorite in or near mining environments. However, normal gem cutting and handling just won’t result in exposure on that scale.
Due to its cleavage, brittleness, and low hardness, fluorite is too fragile for most jewelry use. Ring use isn’t recommended. However, protective settings, occasional wear, and use in pendants and earrings can let you show off these beautiful gems. Some specimens may fade with prolonged exposure to light, so store any fluorite jewelry out of the light. In addition, store them separately from other harder gemstones to prevent contact scratches.
Since fluorites are slightly soluble in water, never submerge them. Clean them only with a warm damp cloth, detergent, and soft brush and never use mechanical cleaning systems. For more cleaning recommendations, consult our gemstone jewelry cleaning guide.
Sterling silver necklace with a pear-shaped fluorite. Photo and jewelry by Gaia Metal Studio. Licensed under CC By-ND 2.0.
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