molybdenite

[muh-lib-duh-nahyt]

molybdenite, a mineral, molybdenum disulfide, MoS₂, blue-gray in color, with a metallic luster and greasy feel. It occurs in crystals of the hexagonal system but more commonly in scales, grains, or foliated or massive form. It has an excellent basal cleavage and the laminae are flexible. It is found in granites, syenites, gneisses, and crystalline limestones. Molybdenite is an important ore of molybdenum. The major sources are quartz veinlets in granite at Climax, Colo., and copper mines in Utah, New Mexico, and Arizona. Minor amounts are recovered in Mexico, Chile, Canada, and Norway.

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Molybdenite

Molybdenite is a mineral of molybdenum disulfide, Mo S₂. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum atoms sandwiched between sheets of sulfide atoms. The Mo-S bonds are strong, but the interaction between the sulfur atoms at the top and bottom of separate sandwich-like tri-layers is weak, resulting in easy slippage as well as cleavage planes.

Molybdenite occurs in high temperature hydrothermal ore deposits. Its associated minerals include pyrite, chalcopyrite, quartz, anhydrite, fluorite, and scheelite. Important deposits include the disseminated porphyry molybdenum deposit at Questa, New Mexico and Climax, Colorado. Molybdenite also occurs in porphyry copper deposits of Arizona, Colorado, Utah, and Mexico.

The element rhenium is always present in molybdenite as a substitute for molybdenum, usually in the parts per million (ppm) range, but often up to 1-2%. High rhenium content results in a structural variety detectable by X-ray diffraction techniques. Molybdenite ores are essentially the only source for rhenium. The presence of the radioactive isotope rhenium-187 and its daughter isotope osmium-187 provides a useful geochronologic dating technique.