Molybdenite

Molybdenite is molybdenum disulfide, the chief ore of the metal molybdenum. It crystallizes in the hexagonal system, typically as soft, flexible, foliated flakes or thin tabular hexagonal plates with a bright metallic, lead-gray to bluish silver-gray sheen.

It is one of the softest minerals, scratched by a fingernail, and feels distinctly greasy or soapy because its layered structure cleaves into slippery sheets — the same property that makes molybdenum disulfide a valued dry lubricant.

Molybdenite looks almost identical to graphite, and the two can be told apart mainly by streak color on glazed surfaces and by molybdenite's slightly higher density and bluish tint.

Molybdenite forms in high-temperature hydrothermal and igneous environments. It is the dominant ore mineral in porphyry molybdenum and porphyry copper-molybdenum deposits, where it precipitates in quartz veinlets and stockworks within altered granitic intrusions.

It also occurs in high-temperature quartz veins, in greisens and pegmatites associated with granite, and in contact-metamorphic skarn zones. Major producing deposits include Climax and Henderson in Colorado, the Bingham Canyon copper mine in Utah, and large operations in China and Chile, where molybdenite is recovered as a byproduct of copper mining.

Look for very soft, flexible silver-gray flakes with a bright metallic luster and a greasy feel that mark the paper or your fingers like graphite. Hardness is only 1-1.5, so a fingernail scratches it easily.

The best way to separate molybdenite from graphite is the streak: molybdenite gives a greenish-gray streak on paper or a bluish-gray to greenish streak on glazed porcelain, whereas graphite leaves a black, more brownish-gray mark. Molybdenite is also denser and shows a faint bluish cast. Its hexagonal plates and association with quartz veins are added clues.

Molybdenite is the world's main source of molybdenum, an alloying metal that adds strength, hardness, and high-temperature and corrosion resistance to steels and superalloys used in pipelines, aerospace, and tools.

Molybdenum disulfide itself is a premier solid lubricant, used as a dry film or oil additive where ordinary greases fail under heat or pressure. The mineral is also a feedstock for molybdenum chemicals and catalysts used in petroleum refining. It has no jewelry use, though collectors value bright crystalline specimens.