Wulfenite

Posted on November 1, 2022 by John J. Bradshaw, GIA GG

INTRODUCTION Wulfenite is a mineral species crystallizing in the tetragonal system, lead molybdate, with the formula PbMoO4. It was named after the Austrian mineralogist, Franz Xavier Wulfen. Wulfenite is almost always found as thin, tabular crystals ranging in color from red-orange to yellow-orange and bright yellow. Mineral specimens are prized by collectors for being attractive and aesthetic (Figure 1). Aside from the vibrant colors in successfully faceted gems, another positive attribute is wulfenite’s high dispersion. The spectral colors are difficult to capture in a photograph (Figure 2) but are truly spectacular in person. As a gemstone, it has no chance of ever being used for jewelry purposes and belongs solely in the collector’s realm. It is rarely faceted for a number of reasons: the thin nature of the crystals do not lend themselves to suitable cutting rough. It is extremely brittle with a hardness of 2.5-3 as well as being heat sensitive and due to the extremely low hardness, even common household dust will scratch specimens or gemstones. FIGURE 1. Wulfenite crystal from the Kaokoveld, Namibia. Photo courtesy of Annett Slade. LOCALITIES/CLARITIES There are many localities across the globe where wulfenite is found but cuttable material is extremely rare and greatly decreases the number of important sources. In the United Sates, the important sources are all in Arizona, namely the Red Cloud Mine in La Paz County (Figure 3), the 79 Mine in Gila County, and the Rowley Mine in Maricopa County. Fine cutting material is occasionally available from Los Lamentos in Chihuahua, Mexico. Wulfenite in larger sizes has been cut from Tsumeb, Namibia. Recent discoveries in the Kaokoveld region of northwest Namibia have produced cutting rough that to date has cut a few unusually large stones (Figure 4). Overall, flawless to eye clean wulfenite gems are the exception rather than the rule. Finished stones often have minor to slightly eye visible inclusions. FIGURE 2. Wulfenite, 3.99 ct from Tsumeb, Namibia. Lighter yellow colors are perfect for showing the high dispersion. Faceted and photo by John Bradshaw, www.rarestone.com STONE SIZES Wulfenite gemstones from Mexico and Arizona rarely exceed 2 ct, although a few exceptional stones have been cut in the 5 ct range. Bright yellow wulfenite from Tsumeb can range up to 10 ct; the largest known weighing 54 ct. From the new workings in Kaokoveld, Namibia, the vast majority of the cut stones are lemon yellow with very few orange gems. Sizes...

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