Wulfenite with Calcite (#84)

Lustrous bright yellow thin blades of wulfenite to 7/8" maximum dimension massed together and partially overgrown with lustrous translucent white complex calcite crystals to 3/8".
North America Lucin District, Box Elder County, Utah 2 ¾" x 2 ¼" x 2 ¼"


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This is our third example of wulfenite in this display - numbers 14 and 47 also feature that mineral.

Wulfenite belongs to the scheelite group of minerals. One of the quests of nearly all scientific endeavors is to classify things so as to discover and make sense of interrelationships among them. Mineralogy is no different. Mineralogists classify minerals into groups whose members are similar in significant ways, which usually means based either on chemistry or crystal structure. The scheelite group consists of four minerals that have the same crystal structure, but are chemically different:

Scheelite   CaWO4
Stoltzite   PbWO4
Powellite   CaMoO4
Wulfenite   PbMoO4

Although they have the same arrangement of atoms (crystal structure), these minerals occur naturally in different geologic environments. Consequently, a complete solid solution range does not occur in nature. Wand Mo substitute freely for one another, though, so there is a partial compositional series between scheelite and powellite, as well as one between stoltzite and wulfenite. (W, by the way, is the chemical symbol for tungsten, Ca is calcium, Pb is lead, and 0 is oxygen.)