WULFENITE ON FLUORITE

ABOUT THE SPECIMEN

Bright orange blades of wulfenite on a chunk of botryoidal fluorite, self-collected by the Aether crew from the Red Cloud Mine in January of 2024. When we found the pocket where this specimen was housed, it took a good deal of careful effort to get it out, and there were only a couple of larger crystals in there. All of the blades just pop out of the contrasting fluorite underneath. What makes this already attractive specimen even more appealing is the glow of the fluorite under both long and shortwave UV light, showing a deep blue and adding a whole new level of contrast. Though the combination of wulfenite on fluorite is relatively common from Red Cloud, they seem difficult to find on the open market, I'd assume due to the difficulty of keeping the pieces together after extraction. 

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Tucked into the Trigo Mountains of Arizona's Sonoran Desert, the Red Cloud Mine is a small silver-lead deposit in which wulfenite crystallized in the oxidized zone above galena as descending groundwater carried dissolved lead and molybdenum downward. What distinguishes Red Cloud from other notable wulfenite localities - Tsumeb, Los Lamentos, Touissit - is a chromatic anomaly traced to trace chromium leached from monzonite country rock in the footwall; chromate ions substituting into the molybdate site of the crystal structure act as a strong orange-red chromophore through a ligand field effect, pushing the color well beyond the yellows and pale oranges that molybdate alone produces. The substitution is essentially a solid solution between wulfenite and the chromate analogue crocoite at the parts-per-thousand level - enough to saturate the color dramatically without detectable crocoite crystallizing separately. Crystals are tabular with the characteristic wulfenite square or rectangular outline; the largest known examples, collected by Ed Over working alone underground in 1938 with minimal equipment, reached roughly 6 cm. Production has always been sporadic and supply perpetually behind demand - a pattern repeating through the original 1880s mining, Over's 1938 finds, a 1996 open-pit operation, and Colorado Calumet's early 2000s work. Fine Red Cloud wulfenites have never been plentiful enough to satisfy the collector market, and old Ed Over material is genuinely rare.