Wulfenite (#47)

Cluster of lustrous thin yellow blades to 5/8" partially encrusted with lustrous translucent white complex calcite xtls. to 1/16".
North America Lucin District, Box Elder County, Utah, USA 1" x 1" x 1"


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The chemical formula of wulfenite is Pb(MoO4). Pb is lead, and Mo is molybdenum. II is a minor ore of molybdenum, an element used in steel alloys and in high temperature applications like heating elements, drills, and saw blades.

The formula could be written entirely correctly without the parentheses: PbMoO4. The reason for using parentheses is that it emphasizes the fact that the molybdenum atoms are surrounded by 4 oxygen atoms in a tetrahedron: (MoO4)2-. This is a characteristic of a great many minerals - a relatively small central atom surrounded by 4 oxygen atoms, yielding a net negative charge to the group. In this case, the negative charge is balanced by the Pb2+ atoms. The largest group of minerals in the crust of the earth, the silicates, is characterized by SiO44- tetrahedra, arranged in a remarkable variety of ways.

The basic classification scheme for minerals is chemical. An xo. group in the formula, where X is some atom like Si, Mo, P, S, or any of several others, means that the name of the chemical classification ends in "-ate" - silicate, molybdate, phosphate, sulfate, and so on. This is very useful, because it tells the scientist and student something important about the mineral (or any chemical compound) right away, using only one word.