Molybdenite is a rare mineral composed of molybdenum and sulphur, with a chemical composition of MoS2. It occurs in igneous and metamorphic rocks as grey hexagonal crystals and foliated masses with a metallic lustre. Molybdenite is the most important ore of molybdenum and often contains minor amounts of rhenium which are often produced as a by-product. Molybdenite has physical properties that often cause it to be confused with graphite. Both of these minerals are grey to silver in colour, have a very low hardness, and occur in hexagonal crystals or foliated masses. Both minerals have a layered atomic structure with planes of extreme weakness. This gives them a slippery feel and makes them valuable as a solid lubricant - ""