Molybdenite

From Wikipedia, the free encyclopedia

Molybdenite

General
Category	Mineral
Chemical formula	molybdenum sulfide:MoS₂
Identification
Color	Black, lead-silvery gray
Crystal habit	Thin, platy hexagonal crystals terminated by pinacoidal faces, also as tapering six-sided pyramids that can be truncated by the pinacoids. Also massive, lamellar and in small grains in sulfide ore bodies
Crystal system	Hexagonal; 6/m 2/m 2/m
Cleavage	[0001] Perfect
Fracture	flaky
Mohs Scale hardness	1 - 1.5
Luster	Metallic
Refractive index	Opaque
Streak	bluish - gray
Specific gravity	4.73
Fusibility	Infusible
Other Characteristics	Thin cleavage sheets and crystals are flexible, but not elastic. It has a greasy feel and leaves marks on fingers

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.

Associated minerals include pyrite, chalcopyrite, quartz, anhydrite, fluorite, and scheelite. Occurs in high temperature hydrothermal ore deposits. Important deposits include the disseminated porphyry molybdenum deposit at Questa, New Mexico. 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.