Wulfenite is a mineral which may be unfamiliar to the novice geologist, but is highly prized by mineral collectors. No other mineral has the strange combination of a vibrant orange color and fiercely sharp rectangular crystals. Although it is too soft and brittle to be used as a gemstone, wulfenite is nonetheless one of the most stunning minerals in all of geology.
Wulfenite has the composition PbMoO4, and so belongs to an unusual class of minerals called “molybdates.” Minerals are divided into classes based on the composition of their anion group. For example, calcite is classified as a carbonate, as its anion group is CO3, and minerals with an SiO2 group are categorized as silicates. Likewise, molybdates all have the anion group MoO4. Wulfenite can form in a “solid solution” with the mineral stolzite, which has the formula PbWO4. The tungsten of stolzite can substitute in for the molybdenum of the wulfenite, thus forming an intermediate mineral solution representing a blend of the two.
Molybdenum’s high melting temperature makes it a useful industrial metal. It is important in oil refinery and when alloyed with iron, increases the strength of steel. Although most molybdenum comes from the appropriately named mineral, molybdenite, wulfenite deposits can also be used as a minor ore of the metal.
Wulfenite is found in the oxidation zone of lead deposits. Oxidation zones are home to some of the world’s strangest and most diverse minerals, as the influence of water and free oxygen interacting with the primary ore body create new and unique minerals. Other minerals associated with wulfenite in the lead ore oxidation zones are: pyromorphite, a bright green, barrel-shaped lead phosphate mineral; vanadinite, a deep crimson, lead vanadate mineral; and mimetite, an often bright yellow, lead arsenate mineral. Combinations of these lead oxidation minerals create other-worldly color combinations, prized by collectors.
Come see our exceptional wulfenite specimen at the Dice Mineralogical Museum, located on the first floor of North Hall, open Wednesdays, Thursdays and Fridays from 12:30 to 4 p.m.!
