Molybdénite
The molybdénite is the sulfide of Molybdène of formula MoS2; its genesis is pneumatolytic, but it can be also presented in the form of a additional Minéral magmatic rocks.
The molybdénite exists into two polytypes:
- * MoS2-2 H , hexagonal, Group of space P63/ mmc
- * MoS2-3 R , trigonal with networks rhomboedric, Group of space R 3 m .
Approximately 80% of the natural molybdénites are 2 H . The Molybdène has a prismatic coordination trigonal
The connection intra-layer is primarily covalent while the interlayer is normally regarded as type Van der Waals, which explains easy cleavage and weak the hardness: 1-1 ½. The Couleur is gray Graphite.
Several metals can replace the Molybdène in small proportion: Niobium, Bismuth, Iron, Copper, money, Lead, Magnesium.
Compared to other sulfides, the molybdénite is a conducting relatively poor, with Résistivité higher than 10-3 Ohm ·m; the Résistivité is very Anisotrope because of the structure in layers.
The crystals of molybdénite are lamellate {00.1}, flexible devices and cleavable in these plans; they resemble of the layers of paper of Aluminum. The molybdénite is the Minéral of most important Molybdène, used like solid lubricant (like the Graphite).
The molybdénite concentrates in the veins of quartz, associated with sulfides of Fer and Nickel: Scheelite, Fluorite and Topaz. Molybdenum is used as element of Alliage for the Acier S.
The tungstenite , WS2, is isostructurelle with the molybdénite and sometimes the two sulfides are associated.
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