Molybdenite
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| Molybdenite | |
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Missing image MolybdeniteUSGOV.jpg Molybdenite (Molybdenum disulfide) | |
| 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 |
| Pleochroism | N/A |
| Streak | bluish - gray |
| Specific gravity | 4.73 |
| Fusibility | Infusible |
| Solubility | ? |
| Other Characteristics | Thin cleavage sheets and crystals are flexible, but not elastic. It has a greasy feel and leaves marks on fingers. |
| Major varieties | |
Molybdenite is a mineral of molybdenum disulfide, MoS2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect which is produced by its structure of close-spaced parallel cleavage planes. Finely powdered MoS2, with particle sizes in the 1-100 µm range, is a common technical dry lubricant. It is also often mixed into various oils or greases, which allows mechanisms so lubricated to run less noisy and to keep running for a while longer even if most of the oil should escape -- very important e.g. in aircraft engines.
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 porphry 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.
References and external links
- Dana's Manual of Mineralogy ISBN 0471032883
- Mineralgalleries.com (http://mineral.galleries.com/minerals/sulfides/molybden/molybden.htm)
- Webmineral (http://webmineral.com/data/Molybdenite.shtml)
- Mindat.org (http://www.mindat.org/min-2746.html)
- Molybdenite Dating (http://www.cnr.colostate.edu/airie/Molybdenite.htm)sk:Molybdenit