Molybdenite

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Molybdenite

Euhedral molybdenite on quartz, Molly Hill mine, Quebec, Canada. The large crystal is 15 mm across
General
Category Sulfide mineral
Formula
(repeating unit)		 MoS2
Strunz classification 02.EA.30
Crystal symmetry Hexagonal dihexagonal dipyramidal
H-M symbol: (6/m 2/m 2/m)
Space group: P 63/mmc
Unit cell a = 3.16 Å, c = 12.3 Å; Z = 2
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
Cleavage Perfect on [0001]
Tenacity Lamellae flexible, not elastic
Mohs scale hardness 1–1.5
Luster Metallic
Streak Bluish gray
Diaphaneity Nearly opaque; translucent in thin flakes
Specific gravity 4.73
Pleochroism Very strong
Fusibility Infusible (decomposes at 1185 °C)
Other characteristics It has a greasy feel and leaves marks on fingers
References [1][2][3][4]

Molybdenite is a mineral of molybdenum disulfide, MoS2. 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 sulfur 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 crystallizes in the hexagonal crystal system as the common polytype 2H and also in the trigonal system as the 3R polytype.[1][2][5]

Crystal structure of molybdenite

Occurrence

A sample of molybdenite mineral less pure than the single-crystal specimen at right.

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 deposits at Questa, New Mexico and the Henderson and Climax mines in Colorado. Molybdenite also occurs in porphyry copper deposits of Arizona, 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.

Semiconductor

Molybdenite flakes are a direct bandgap semiconductor with good charge mobility and can be used to create small or low-voltage transistors[6] possibly more easily than using graphene.

The transistors can emit light and may have future use in optoelectronics.[7]

See also

References

  1. ↑ 1.0 1.1 Handbook of Mineralogy
  2. ↑ 2.0 2.1 Mindat.org
  3. ↑ Webmineral data for Molybdenite
  4. ↑ Dana's Manual of Mineralogy ISBN 0-471-03288-3
  5. ↑ Molybdenite 3R on Mindat
  6. ↑ "Molybdenite transistor is a first". 8 Feb 2011. 
  7. ↑ First light from molybdenite transistors. 19 Apr 2013
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