1911 Encyclopædia Britannica/Molybdenite
MOLYBDENITE, a mineral consisting of molybdenum disulphide, MoS2. It closely resembles graphite in appearance, but may readily be distinguished from this by its greater density (4·7) and by its behaviour before the blowpipe. Crystals have the form of six-sided plates or scales, but they are never sharply defined, and their reference to the hexagonal system is doubtful. They have a perfect cleavage parallel to the large surface of the plates, and the flakes are readily bent, but are not elastic. The mineral is very soft (H= 1 to 112) and unctuous, and makes a bluish-grey mark on paper: it is opaque and has a bright metallic lustre. The colour is lead-grey differing slightly from that of graphite in having a bluish tinge. The name molybdenite is from the Greek μόλυβδος, meaning lead or lead ore, with which graphite (black-lead) and molybdenite were confused; the latter was distinguished by P. J. Hjelm, who in 1782 discovered the element molybdenum in this mineral.
Molybdenite occurs as disseminated scales in crystalline rocks—such as granite, gneiss, schist and marble—and also in quartz-veins. It has been found in small amounts at many localities, but only those which have yielded large crystals need be specially mentioned here, viz. in a pyroxene-rock at Aldfield in Pontiac county, Quebec; with native bismuth at Kingsgate in Gough county, New, South Wales; with wolframite and scheelite in quartz-veins at Caldbeck Fells in Cumberland; and recently, as crystals 6 in. across, at Slangsvold near Raade in Norway.
Molybdenite has been used mainly for the preparation of molybdates for use as chemical reagents. Recently, however, it has been used in the manufacture of molybdenum steel (ferro-molybdenum), which by reason of its hardness and toughness is specially suitable for tools. (L. J. S.)