Molybdenite is a molybdenum sulfide mineral (MoS2). It has hexagonal crystals, metallic luster, a bright silvery color, and a dark gray streak. It is fairly soft (H=2) and has one cleavage. Molybdenite is especially distinctive in being flexible - thin scales or plates of the stuff will easily bend but won't snap back into shape like biotite or muscovite mica.
Molybdenite is nearly identical to graphite (C) in its physical characteristics. Graphite is a principally a metamorphic mineral. Molybdenite is usually an igneous mineral, occurring in hydrothermal veins and pegmatites. It also occurs in some contact metamorphic rocks (skarns).
Molybdenite in quartz-rich pegmatite (above & below; above: 5.1 cm tall; below: 4.1 cm across) from the Moly Hill Mine, near Malartic, Preissac Township, southwestern Quebec, Canada.
The pegmatite intrudes the Preissac-Lacorne Batholith (Abitibi Greenstone Belt, late Neoarchean, 2.630-2.675 billion years).
Dark silvery-gray = molybdenite; glassy whitish-gray = quartz; shiny brownish-gray in sample shown below = muscovite mica.