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.
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 molybdenumdisulfide, 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.
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.
Molybdenumdisulphide is naturally found in the form of molibdnite mineral and has an appearance very similar to graphite.
Molybdenum sulphide is not very soluble in water while it easily dissolves in acqua regia (mixture of nitric acid and hydrochloric acid) and hot water in some inorganic acids like nitric, sulphuric and hydrochloric acid.
To qualify as a lubricant grade, the MolybdenumDisulphide must be produced to very high purity tolerances and graded according to the level of residual contaminate, particularly silicon and iron.
MolybdenumDisulphide is a unique lubricant in its own right, and is often used in powdered form to be burnished (polished) onto bearing surfaces and components for total life lubrication or as an assembly compound.
The MolybdenumDisulphide Powder is very frequently included into grease formulations to improve extreme pressure load carrying capacity of a grease, to improve its shock load carrying capacity and anti wear properties.
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