Molybdenite (MoS₂) is the primary ore of molybdenum, valued for its role in strengthening steel alloys and as a catalyst in desulfurization. Mining occurs as both primary molybdenum operations and as a by-product of copper porphyry deposits. Ore is concentrated by flotation, then roasted to produce molybdenum oxide for steel and chemical industries. Top producers include China, the U.S., Chile, and Peru. Much production comes from copper mines with molybdenum by-product credits, making molybdenite output tied to copper mining activity. Primary molybdenum mines add flexibility but are fewer in number.