Molybdenite crystal structure

Fuerstenau (1980) found that sulphide minerals are naturally floatable in the absence of oxygen. Yoon (1981) ever attributed the natural floatability of some sulphide minerals to their very low solubility. Finkelstein et al. (1975) considered that the natural floatability of sulphide minerals are due to the formation of elemental sulphur and related to the thickness of formation of elemental sulphur at the surface. Some authors reported that the hydrophobic entity in collectorless flotation of sulphide minerals were the metal-deficient poly sulphide (Buckley et al., 1985). No matter whichever mechanism, investigators increasingly concluded that most sulphide minerals are not naturally floatable and floated only under some suitable redox environment. Some authors considered that the natural floatability of sulphide minerals was restricted to some special sulphide minerals such as molybdenite, stibnite, orpiment etc. owing to the effects of crystal structure and the collectorless floatability of most sulphide minerals could be classified into self-induced and sulphur-induced floatability (Trahar, 1984 Heyes and Trahar, 1984 Hayes et al., 1987 Wang et al., 1991b, c Hu et al, 2000). 

The most controversial and contradicting problem is, perhaps, the natural and collectorless floatability of sulphide minerals. Gaudin (1957) classified the natural hydrophobicity of different minerals according to their crystal structure and showed that most sulphide minerals were naturally hydrophobic to some extent, which had been fiirther proved based on van der Waals theory by Chander (1988, 1999). Lepetic (1974) revealed the natural floatability of chalcopyrite in dry grinding. Finklestein (1975, 1977) demonstrated that orpiment, realgar and molybdenite were naturally floatable, and that pyrite and chalcopyrite had natural floatability at certain conditions due to the formation of surface elemental sulphur. Buckley and Woods (1990,1996) attributed the natural floatability of chalcopyrite... 

The 2 3TPT Layer Crystal Structure of Molybdenite [M0S2]... 

Takeuchi, Y., Nowacki, W. Detailed crystal structure of rhombohedral M0S2 and systematic deduction of possible polytypes of molybdenite. Schweiz. Mineral. Petrog. Mitt. 44, 105—... 

The crystal structure of natural molybdenite has been shown to be hexagonal, with six-fold symmetry, two molecules per unit cell, and a laminar, or layer-lattice... 

Takeuchi, Y. and Nowacki, W., Detailed Crystal Structure of Rhombohedral M0S2 and Systematic Deduction of Possible Polytypes of Molybdenite, Schweiz Mineral. Petrographische Mittellungen, 44, 105, (1964). 

FIGURE 6.14 The crystal structure of molybdenite. The S ions stack AABB while the Mo ions occupy half the trigonal prisms in each S sandwich . 

Dickinson, R. G., and L. Pauling. 1923. The crystal structure of molybdenite. Journal of the American Chemical Society 45 1466-1471. 

Figure 10.1 The Top and Side Views of the Crystal Structure of the 2H-M0S2 Molybdenite.

T ike metals minerals also exhibit typical crystalline structures. As an example, the structure of molybdenite is shown in Figure 1.17. It is hexagonal with six-pole symmetry and contains two molecules per unit cell. Each sulfur atom is equidistant from three molybdenum atoms and each molybdenum atom is surrounded by six sulfur atoms located at the comers of a trigonal prism. There are two types of bonds that can be established between the atoms which constitute the molybdenite crystal stmcture. They are the covalent bonds between sulfur and molybdenum atoms and the Van der Waals bonds between sulfur-sulfur atoms. The Van der Waals bond is considerably weaker than the covalent sulfur-molybdenum bond. This causes the bonds of sulfur-sulfur to cleave easily, imparting to molybdenite the property of being a dry lubricant. Molybdenite adheres to metallic surfaces with the development of a molecular bond and the friction between metallic surfaces is replaced by easy friction between two layers of sulfur atoms. 

Fig. 5-14.—The structure of the hexagonal crystal molybdenite, MoSt, showing the arrangement of sulfur atoms (large circles) at the corners of a trigonal prism about each molybdenum atom (small circles).

The disulfide (WS2) is the only stable compound which can be synthesized directly from the elements. Previous literature data are compiled in Refs.6-8 The W—S system presented in Fig. 9 is based on literature data and schematically illustrates possible phase relations. Normally, WS2 crystallizes hexagonally and has the same structure as molybdenite under certain conditions, however, a rhombohedral... 

Molybdite or molybdenum ochre forms orthorhombic crystals, and occurs with molybdenite, from which it is probably derived. It consists essentially of the trioxide MoOg, but analysis has shown that its composition is probably expressed by the formula Fe203-3Mo03.7jH20 it being, in fact, a hydrated ferric molybdate. The sample examined was of a yellow colour, possessed a fibrous structure and a silky lustre, and was pleochroic. 

Even without atomic resolution, AFM has proved its worth as a technique for the local surface structural determination of a number of bio-inorganic materials, such as natural calcium carbonate in clam and sea-urchin shells [123]. minerals such as mica [124] and molybdenite [125] as well as the surfaces of inorganic crystals, such as silver bromide [126] and sodium decatungstocerate [127]. This kind of information can prove invaluable in the understanding of phenomena such as biomineralization, the photographic process or catalysis, where the surface crystallography, especially the presence of defects and superstructures, can play an important role, but is difficult to determine by other methods. AFM has the considerable advantage that it can be used to examine powdered samples, either pressed into a pellet, if the contact mode is employed, or loosely dispersed on a surface, if intermittent or non-contact AFM is available. 

The first TEM studies of defects in minerals were mostly carried out on layer-structured crystals that could easily be cleaved to electron transparent thicknesses. These included mica [33], graphite [34], molybdenite [35,36], and talc [37]. The study of dislocation networks in talc [38] is an early milestone in dislocation analysis. Thereafter, the ion-rmllmg method (and, more recently, the FIB (focused ion beam) technique) made it possible to investigate dislocations and other defects in a wide range of minerals, crustal rocks, and extraterrestrial materials. 

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