MOLYBDENITE, a mineral consisting of molybdenum di sulphide, 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= i to 1.5) 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 is from Gr. 6XvfThos , 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 is fairly common in small quantities as one of the first
minerals formed in high-temperature veins, along with tinstone, wolframite and bismuth compounds. The commercially workable deposits, however, belong to several different types, as follows : In pegmatites and quartz-veins associated with granite, e.g., Canada, Saxony and Telemarken, Norway; as segregations in granite, e.g., Moss mine, Quyon, Quebec ; in metamorphic zones at the contact of granite and limestone (contact pyroxenite), Pon tiac county, Quebec; in pipes of granite, with wolfram and bis muth, Queensland and the New England area of New South Wales. Molybdenite has been used mainly for the preparation of mo lybdates for use as chemical reagents, and also in the manufacture of molybdenum steel (ferro-molybdenum), which by reason of its hardness and toughness is specially suitable for tools.