Molybdenum is a rare metal, silvery-white in color, brittle and very difficult to fuse. It is used mostly as an alloy of steel, to make certain grades of tool steel. The world’s greatest supply is obtained from Climax, Colorado, where the principal ore mineral is molybdenite.
[Molybdenite]
MoS₂
Occurs in scales or scaly masses, occasionally in tabular hexagonal crystals; hardness 1.5; specific gravity 4.7; color lead-gray; streak bluish-gray; luster metallic; opaque.
This mineral is the chief source for the metal molybdenum. Its extreme softness and greasy feel will distinguish it at once from any other mineral except graphite, which has much the same qualities, but its scaly character and the more bluish tinge in streak and color will distinguish these two.
It occurs in granites, gneisses, and metamorphic rocks in Colorado, New Mexico, Maine, Connecticut, New Hampshire, New York, Pennsylvania, etc.
Antimony
Antimony is another hard, brittle metal, of bluish-white color. Exposed to the air at ordinary temperatures it does not tarnish; and this combined with its hardness make it useful for such alloys as Britannia metal, type metal, and pewter. Only one of its minerals, stibnite, is common enough for mention.
[Stibnite]
Sb₂S₃
[Pl. 25]
gray antimony
Occurs in prismatic or needle-like crystals; hardness 2; specific gravity 4.5; color lead-gray; streak lead-gray; luster metallic; opaque.
The crystals of stibnite are orthorhombic and usually elongated, the sides striated and the ends with low pyramids on them. Sometimes the long crystals are curved or even twisted. There is a well-developed cleavage parallel to face b in the figure. While the color is similar to that of galena, the form and cleavage are so different that stibnite is easily determined.