Emerald-cut wulfenite, 2.53 cts, Red Cloud Mine, Arizona. Photo © Joel E. Arem, PhD, FGA. Used with permission.
Although aesthetically magnificent wulfenite crystals are often too thin, soft, and sensitive to cut for jewelry, rare faceted pieces are greatly prized by collectors. The red of wulfenite, especially from the Red Cloud Mine in Arizona, is one of the richest colors in nature.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
| Data | Value |
|---|---|
| Name | Wulfenite |
| Colors | Orange (various shades), brownish orange, yellow, brownish yellow, yellow-orange, red, brown, yellowish gray, tan, greenish brown. |
| Crystallography | Tetragonal. Crystals commonly tabular with square outline; also pyramidal; massive, granular. |
| Refractive Index | 2.283-2.405 |
| Luster | Resinous to adamantine. |
| Hardness | 2.5-3 |
| Fracture | Uneven to subconchoidal |
| Specific Gravity | 6.5-7.0 |
| Birefringence | 0.122 |
| Cleavage | Distinct 1 direction |
| Dispersion | 0.203 |
| Heat Sensitivity | Yes. |
| Luminescence | None. |
| Luminescence Present | No |
| Transparency | Transparent to translucent. |
| Absorption Spectrum | Not diagnostic. |
| Formula |
PbMoO4 |
| Pleochroism |
Weak, in orange to yellow tints. |
| Optics |
o = 2.405; e = 2.283. Uniaxial (-). May show anomalously biaxial character. |
| Optic Sign | Uniaxial - |
| Etymology |
After the Austrian mineralogist, Franz Xavier Wulfen, who wrote a lengthy monograph in 1785 on the lead ores of Carinthia, Austria. |
| Occurrence |
Secondary mineral in the oxidized zone of ore deposits. |
Orange wulfenites on red-orange mimetite, 3.5 x 2.6 x 2.2 cm, San Francisco Mine, Cucurpe, Sonora, Mexico. © Rob Lavinsky, www.iRocks.com. Used with permission.
Wulfenite and stolzite form a mineral series, as the molybdenum (Mo) and tungsten (W) analogues, respectively.
Many localities across the globe produce wulfenites. However, cuttable material is very rare, indeed. Individual crystals usually have a tabular structure. As a result, they’re frequently too thin to find a fragment suitable for cutting. Should a faceter acquire a suitable piece, even more challenges await. These beautiful gems combine very low hardness with sensitivities to both heat and vibration. Although not well suited for jewelry use, faceted pieces, as well as crystals, make stunning collector’s gems.
The wulfenites in this specimen contain inclusions that make one side of their crystal surfaces brown. The other sides are lustrous red. 8.3 x 7.3 x 4.6 cm, source near Urumqi, Kuruktag Mountains, Xinjiang Uygur Region, Northern China. © Rob Lavinsky, www.iRocks.com. Used with permission.
Red wulfenites over 1 carat and yellowish or orange stones over 2 carats are extremely scarce. The only larger stones come from Namibian (Tsumeb) material. However, this locality produced very few facetable gems very infrequently. Thus, faceters have cut very few stones from this source.
Wulfenite, 4.0 cts, Tsumeb, Namibia. Photo © Joel E. Arem, PhD, FGA. Used with permission.
Wulfenites may show an anomalous biaxial optic character.
Under physical pressure, some wulfenite crystals may generate an electric charge. This is known as the piezoelectric effect.
Wulfenite: Arizona (gem ~ 1.5, crystal 1 inch long, Red Cloud Mine). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Laboratories have synthesized both wulfenites and stolzites through pulled (Czochralski) and flux methods. Sintering cerussite with molybdite (a mineral source of Mo) has also produced synthetic wulfenites. While these synthetics have industrial uses, they have also appeared as attractive crystals and even faceted pieces.
Synthetic wulfenite, 84.7 cts. © Joel E. Arem, PhD, FGA. Used with permission.
None known.
Wulfenites, 5.94 and 6.11 cts, Tsumeb, Namibia. Photo © Joel E. Arem, PhD, FGA. Used with permission.
Notable gem-quality sources include the following:
Rough and cut set, wulfenite crystal and modified octagonal-cut gem, 4.3 x 3.2 x 2.7 cm (crystal), 1.32 cts (gem). Ahumada Mine, Los Lamentos, Chihuahua, Mexico. © Rob Lavinsky, www.iRocks.com. Used with permission.
Occasionally, U.S. localities produce crystals both thick and transparent enough for faceting. These include, most notably, the Red Cloud Mine and the Seventy-Nine Mine in Arizona as well as other sources. Some of these crystals have yielded gems up to about 5 carats.
Tsumeb, Namibia has produced crystals several inches across. This material has yielded faceted gems over 50 carats in size.
Wulfenite: Tsumeb, Namibia (21+). Photo © Joel E. Arem, PhD, FGA. Used with permission.
With a hardness of 2.5 to 3, knives and copper coins could scratch wulfenites. (By comparison, household dust, which contains silicon quartz, has a hardness of 7). You’re more likely to find wulfenites in mineral collections than in jewelry collections. Treat any specimens delicately.
Consult our gemstone jewelry cleaning guide for more care recommendations.
Rough and cut set, wulfenite crystal and freeform step eye-cut, 2.0 x 1.1 x 0.3 cm (crystal), 1.02 cts (gem). Red Cloud Mine, La Paz County, Arizona. © Rob Lavinsky, www.iRocks.com. Used with permission.
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