Molybdenite

Molybdenum Sulfide
MoS₂

Molybdenite is a very soft metallic mineral. It can be easily confused with graphite, but not with many other minerals. Graphite has a darker black-silver color and a black-gray to brown-gray streak, whereas molybdenite has a bluish-silver color and streak. Unfortunately, the difference is so slight that it is recommended that the two minerals be seen side by side. Their respective streaks should also be observed side by side to appreciate the differences. If larger samples, free of host rock, are available, then the greater density of molybdenite can be used for identification.

Molybdenite's structure is composed of molybdenum ions sandwiched between layers of sulfur ions. The sulfur's layers are strongly bonded to the molybdenum, but are not strongly bonded to other sulfur layers, hence the softness and perfect cleavage. It is soft enough to leave a mark on paper and fingers. Its greasy feel is due to its extreme softness. Molybdenite or "Moly Ore" as it is sometimes called, is a very high luster mineral and can be an interesting mineral to add to a collection.