Molybdenite

Molybdenite
Euhedral molybdenite on quartz, Molly Hill mine, Quebec, Canada. The large crystal is 15 mm across
General
Category	Sulfide mineral
Formula (repeating unit)	Molybdenum disulfide (MoS2)
Strunz classification	2.EA.30
Crystal system	Common, 2H polytype: hexagonal 3R polytype: trigonal
Crystal class	2H polytype: dihexagonal dipyramidal (6/mmm) 3R polytype: Ditrigonal pyramidal (3m)
Space group	2H polytype: P63/mmc 3R polytype: R3m
Unit cell	2H polytype: a = 3.16 Å, c = 12.3 Å; Z = 2 3R polytype: a = 3.16 Å, c = 18.33 Å; Z = 3
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
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

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.

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.