Molybdenite is a natural mineral form of molybdenum disulfide that contains molybdenum and is used in steel production. It has a layered structure of molybdenum atoms sandwiched between sulfur atoms.

Molybdenite is extremely soft with a metallic luster, and is superficially almost identical to graphite, to the point where it is not possible to positively distinguish between the two minerals without scientific equipment. It marks paper in much the same way as graphite. Its distinguishing feature from graphite is its higher specific gravity, as well as its tendency to occur in a matrix.

Molybdenum improves the strength, hardness, and corrosion resistance of metals.