Villiaumite Value, Price, and Jewelry Information

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Custom cushion-cut villiaumite, 4.49 cts, 10.3 x 8.8 mm, Mont-Saint Hilaire, Quebec, Canada. © The Gem Trader. Used with permission.

A little-known and rare collector’s gemstone, villiaumite is very difficult to facet. Its toxicity also makes it inadvisable to handle or wear.

Villiaumite Information

Data Value
Name Villiaumite
Formula NaF
Colors Deep carmine-red, brownish red, lavender pink to light orange; becomes colorless if heated to 300° C.
Hardness 2-2.5
Cleavage Perfect 1 direction
Crystallography Isometric; crystals tiny; usually massive, granular.
Refractive Index 1.327. Guinea material: 1.330-1.332
Birefringence None.
Luminescence May show dark red to orange and yellow fluorescence under UV (SW and LW).
Luminescence Present Yes
Absorption Spectrum 510 nm (carmine red)
Pleochroism Anomalous, strong: yellow/pink to deep carmine-red.
Optics N = 1.327. Isotropic. May show anomalous birefringence.
Luster Vitreous
Specific Gravity 2.79
Enhancements Heating may turn colored gems colorless. Gamma radiation may turn colorless crystals brown.
Typical Treatments Heat Treatment, Irradiation
Transparency Transparent to translucent
Heat Sensitivity Yes
Luminescence Type Fluorescent, UV-Long, UV-Short
Etymology After the French explorer M. Villiaume, in whose collection of rocks from Guinea the material was first discovered.
Occurrence In alkalic rocks, such as nepheline syenites.
villiaumites - Namibia

Villiaumites in igneous rock matrix, crystals up to 1 cm in length, Aris Phonolite, Aris, Khomas Region, Namibia. © Rob Lavinsky, www.iRocks.com. Used with permission.

Does Villiaumite Make a Good Jewelry Stone?

Villiaumites present several major problems for jewelry use. With a hardness of just 2-2.5, these stones could be scratched easily. Their perfect cleavage makes them susceptible to breaking. They’re also water soluble. These properties make them not only inadvisable to wear but also difficult to cut. Faceters have used special tricks to facet villiaumite, such as using alcohol as a cutting coolant instead of water.

Villiaumites are also heat sensitive. Stones heated to 300° C (572° F) become colorless. Jewelry torches can easily exceed that temperature. 

You’re more likely to find villiaumites in mineral collections, if at all, than jewelry collections. Although first described in 1908, villiaumite remains relatively unknown among collectors of rare gemstones because no facetable material was reported until 1976. This rough, from the Los Islands, Guinea, was cut into tiny gems with deep red color. Since then, other sources have produced larger, facetable villiaumites in more colors. However, they remain very rare. Faceted villiaumites would appeal most to collectors of unusual gems or aficionados of the art of gem cutting.

villiaumite - Namibia

Faceted crystal villiaumite, 1.47 cts, 9 x 6.5 mm, Namibia. © The Gem Trader. Used with permission.

Is Villiaumite Hazardous?

Villiaumite, as sodium fluoride, also poses a significantly more serious problem to faceters, gem and mineral collectors, and jewelry enthusiasts: it’s toxic. Villiaumite’s water solubility makes it especially dangerous, since aqueous solutions of sodium fluoride are readily absorbed by the human body. Accidentally inhaling or ingesting villiaumite particles can cause serious health problems or even death. Contact with this mineral can also cause skin, eye, and respiratory irritation. Wash your hands after handling any mineral specimen or finished gem.

Jewelry use is not recommended.

Consult the Material Safety Data Sheet (MSDS) for sodium fluoride for more information on villiaumite’s hazards and safety recommendations, including storage recommendations.

The IGS doesn’t recommend cutting this material. For an illuminating discussion specifically on faceting villiaumites, see this thread from the GemologyOnline.com forum. For information on general lapidary safety, consult our articles on safety tips and toxic gems.

Identifying Villiaumites

Villiaumite’s toxicity and sensitivities may make some standard gemological tests risky. For example, in 2020, Kenneth Scarratt of the ICA GemLab examined an orange, rectangular step-cut villiaumite. Opting not to conduct a refractometer reading, which would involve putting the stone in contact with fluids, he instead used the Duc de Chaulnes’ method. This technique measures the refractive index (RI) by dividing the real depth of the gem, from table to keel in mm, by the apparent depth, measured using a microscope fitted with a mm scale.

Measuring the RI of the specimen is a useful test. As Scarratt also notes, villiaumite’s RI measures significantly lower than those of other gemstones and even below that of water.

Although villiaumites are singly refractive, some specimens may show anomalous double refraction (ADR) and even strong anomalous pleochroic colors. An examination with a dichroscope or polariscope can confirm ADR.

Are There Synthetic Villiaumites?

Scientists have synthesized villiaumites. This lab-created material is colorless. However, there’s no known jewelry use for this material (and clearly little incentive for it).

Gemstone treatments for villiaumites are also very unlikely. However, a study has indicated that colorless villiaumite crystals in fluid inclusions in an unspecified host mineral turned brown when exposed to gamma radiation. As noted earlier, villiaumites can also turn colorless if exposed to temperatures over 300° C.

Where are Villiaumites Found?

The Los Islands, Guinea, the type locality for villiaumite, have produced facetable material, reddish crystals in nepheline syenite. Their RIs range somewhat higher than specimens from other sources, from 1.330 to 1.332.

villiaumites in nepheline syenite - Guinea

Villiaumites in nepheline syenite, Rouma, Los Islands, Conakry, Guinea. Photo by David Dyer. Public Domain.

The following sites have also produced facetable villiaumites:

  • Francon Quarry, Mont-Saint Hilaire, Quebec, Canada.
  • Aris, Khomas Region, Namibia.
  • Kola Peninsula, Russia.

Other notable sources include the following:

  • Minas Gerais, Brazil; Greenland; Colorado, New Mexico, United States.
villiaumites - Brazil

Carmine red villiaumites, crystals up to 3 mm, with tuperssuatsiaite, makatite, microcline, apophyllite-(KF), and hainite on phonolite. Pedreira Bortolan, Pocos de Caldas, Minas Gerais, Brazil. © Rob Lavinsky, www.iRocks.com. Used with permission.

How Large Can Villiaumites Get?

Guinea villiaumites might yield gemstones up to two carats. Despite their small size, they’re desirable because so few stones exist. Canada, Namibia, and Russia have produced larger gemstones.

  • Smithsonian Institution (Washington, DC): 1.21 (orange-red, Guinea).
  • Private Collection: 12.1 (red, Quebec, cabochon?).
rectangle-cut villiaumite - Russia

Custom rectangle-cut villiaumite, 3.48 cts, 9.2 x 8.2 mm, Kola Peninsula, Russia. © The Gem Trader. Used with permission.

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