Molybdenite, molybdenum sulfide, is the chief ore of the element molybdenum. It is a silvery-black mineral that occurs as scattered grains and also sometimes in well-formed hexagonal shaped crystals. Molybdenite is very soft, sectile (you can cut it with a pocket knife), and flexible (the flat crystals can be bent without breaking). Molybdenite occurs in many localities, but never in large quantities. The crystals from Chelan, Washington are as fine as those from any locality.