Sphalerite form

Zinc sulfide is white to gray-white or pale yellow powder. It exists in two crystalline forms, an alpha (wurtzite) and a beta (sphalerite). The wurtzite form has hexagonal crystal structure refractive index 2.356 density 3.98 g/cm3 melts at 1,700°C practically insoluble in water, about 6.9 mg/L insoluble in alkalis soluble in mineral acids. The sphalerite form arranges in cubic crystalline state refractive index 2.368 density 4.102 g/cm changes to alpha form at 1,020°C practically insoluble in water, 6.5 mg/L soluble in mineral... 

STRUCTURE. CdSe forms the same three crystal stractures as described earlier for CdS. The main difference between the CD films of the two materials is that, while CdS can be commonly found in both the wurtzite and sphalerite forms, CdSe is more commonly deposited in the cubic zincblende form. Mixtures of the two forms have been reported in some cases, particularly when a visible Cd(OH)2 precipitate is present in the initial deposition solution. 

Many IIA-sulphides and -oxides as well as IIIA-nitrides crystallize in the wurtzite form, but some of them (ZnS, of course, but also CdS, GaN and others) can also be found in the sphalerite form. SiC can adopt the wurtzite form (2//-SiC) or less frequently the sphalerite form (3C -SiC), with a notable difference in the band gap (3.3 or 2.3 eV, respectively), but when grown by vapour-phase epitaxy, SiC is usually obtained in the form of polytypes with... 

Krunks et al. [119] studied zinc thiocarbamide chloride as a single-source precursor for obtaining thin films of zinc sulfide by spray pyrolysis. By heating this compound to 1200 C, they demonstrated that cubic ZnS (sphalerite) forms below 300 °C and stays in this form until 760 C, when it transforms to hexagonal ZnS (wurtzite). 

Figure 14.1 shows each crystal stmcture. It has been reported that electroluminescent material must contain both sphalerite and wurtzite phases (Arterton et al.,1992). The wurtzite type stmcture predominates when the bonding is primarily ionic whereas the more covalent systems favor the sphalerite form. The cubic phase of ZnS is not grown as easily as the hexagonal phase, thus making the hexagonal phase more appealing for EL device applications (Bellotti et al., 1988). 

Metastable phases such as amorphous silica (SiOa) and wurtzite (ZnS) are common in mid-oceanic ridge deposits. These phases form fi om highly supersaturated mixed fluid of hydrothermal solution and seawater. Solubility of metastable phases is higher than that of stable phases. Therefore, metastable phases dissolve and stable phases form after the formation of ore deposits. Wurtzite (metastable phase of ZnS) is observed in active chimney, but sphalerite (stable phase of ZnS) is in nmiactive chimney. It is inferred that sphalerite formed by the dissolution of wurtzite. 

The principal ores of zinc are sphalerite (sulfide), smithsonite (carbonate), calamine (silicate), and franklinite (zine, manganese, iron oxide). One method of zinc extraction involves roasting its ores to form the oxide and reducing the oxide with coal or carbon, with subsequent distillation of the metal. 

Alaska, Washington, and Nevada. Ores of the Southeast Missouri lead belt and extensive deposits such as in Silesia and Morocco are of the replacement type. These deposits formed when an aqueous solution of the minerals, under the influence of changing temperature and pressure, deposited the sulfides in susceptible sedimentary rock, usually limestone and dolomites. These ore bodies usually contain galena, sphalerite, and pyrite minerals, but seldom contain gold, silver, copper, antimony, or bismuth. 

When the radius ratio of an ionic compound is less than about 0.4, corresponding to cations that are significantly smaller than the anion, the small tetrahedral holes may be occupied. An example is the zinc-blende structure (which is also called the sphalerite structure), named after a form of the mineral ZnS (Fig. 5.43). This structure is based on an expanded cubic close-packed lattice of the big S2 anions, with the small Zn2+ cations occupying half the tetrahedral holes. Each Zn2+ ion is surrounded by four S2 ions, and each S2" ion is surrounded by four Zn2+ ions so the zinc-blende structure has (4,4)-coordination. 

FIGURE 5.43 Hie zinc-blende (sphalerite) structure, rhe tour zinc ions (pink) form a tetrahedron within a face-centered cubic unit cell composed of sulfide ions (vellow).The zinc ions occupy half the tetrahedral holes between the sulfide ions, and the parts or the unit cell occupied by zinc ions are shaded blue. The detail shows how each zinc ion is surrounded by four sulfide ions each sulfide ion is similarly surrounded by four zinc ions. 

Sulfur is widely distributed as sulfide ores, which include galena, PbS cinnabar, HgS iron pyrite, FeS, and sphalerite, ZnS (Fig. 15.11). Because these ores are so common, sulfur is a by-product of the extraction of a number of metals, especially copper. Sulfur is also found as deposits of the native element (called brimstone), which are formed by bacterial action on H,S. The low melting point of sulfur (115°C) is utilized in the Frasch process, in which superheated water is used to melt solid sulfur underground and compressed air pushes the resulting slurry to the surface. Sulfur is also commonly found in petroleum, and extracting it chemically has been made inexpensive and safe by the use of heterogeneous catalysts, particularly zeolites (see Section 13.14). One method used to remove sulfur in the form of H2S from petroleum and natural gas is the Claus process, in which some of the H2S is first oxidized to sulfur dioxide ... 

Huggins (1922) was the first investigator to assign structures to sphalerite, wurtzite, chalcopyrite, pyrite, marcasite, arsenopyrite, and other sulfide minerals in which each sulfur atom forms four tetrahedrally directed covalent bonds with surrounding atoms. These structures would be described as involving quadricovalent argononic S2+. 

Another tj je of stacking fault is called "poljretructure". A good example is ZnS, which is dimorphic (has two forms). The cubic form of ZnS is called sphalerite, whereas the hexagonal form is CciUed wurtzite (These are their mineral names, aifter the first geologist who discovered them). The stacking sequence for sphalerite is AB or ABBA that for wurtzite is ABC. A polystructure sometimes results when sphalerite is converted to wurtzite ... 

Marutani and Takenouchi (1978) clarified the variations in homogenization temperature and salinity of inclusion fluids in quartz from stockwork siliceous orebodies at the Kosaka mine (Fig. 1.35 Urabe, 1978). They showed that the temperature decreases stratigraphically upwards from stockwork ore zone (280-320°C) to bedded ore zone (260-310°C). Pisutha-Arnond and Ohmoto (1983) carried out fluid inclusion studies of the stockwork siliceous ores from five Kuroko deposits (Kosaka, Fukazawa, Furutobe, Shakanai, and Matsumine) and revealed that black ore minerals (sphalerite, galena, barite) and yellow ore minerals (chalcopyrite, quartz) formed at 200-330°C and 330 50°C, respectively, and salinities of the ore fluids remained fairly constant at about 3.5-6 equivalent wt% NaCl. They analyzed fluids extracted from sulfides and quartz Na = 0.60 0.16 (mol/kg H2O), K = 0.08 0.05, Ca = 0.06 0.05, Mg = 0.013 0.008, Cl = 0.82 0.32, C (as CO2) = 0.20 0.15 and less than 6 ppm each for Cu, Pb, Zn and Fe. 

The good correlation between homogenization temperatures and electrum-sphalerite temperatures suggests several points (1) the uncertainties of electrum-sphalerite temperatures are less than 20° to 30°C, even at temperatures from ca. 180° to 300°C, (2) the electrum-sphalerite-pyrite-argentite assemblage was formed close to equilibrium in Japanese epithermal Au-Ag vein-type deposits, and (3) the pressure corrections to homogenization temperatures for Japanese epithermal Au-Ag vein-type deposits is small, less than 20°C to 30°C. 

The chemical compositions of coexisting sphalerite and tennantite-tetrahedrite from the mines were determined. Except the Ashio polymetallic deposits, the other deposits have been formed at late Cretaceous related to felsic magmatism. 

Motomura, T. (1986) Chemical composition of electrum and sphalerite from the Inakuraishi-type Mn deposits. In Effect of Ore-Forming Environment on the Ore Texture, Mineral Features and Mineral Assemblage. Symposium held at Ito City, Japan 1986 (in Japanese). 

It is noteworthy that bornite, chalcocite and tetrahedrite-tennantite which are common minerals in Kuroko deposits occur in gold bearing Besshi-type deposits. Although these minerals are considered to be secondary minerals, depositional environments of these minerals are characterized by higher /s, and foj conditions. It is also noteworthy that these deposits are rich in pyrite rather than pyrrhotite. Probably, Besshi-subtype deposits in Shikoku formed under the higher fo and /sj conditions than the deposits characterized by pyrrhotite (Maizuru, Hidaka, Kii, east Sanbagawa). Such typical Besshi-type deposits (Besshi-subtype deposits in Shikoku) are characterized by simple sulfide mineral assemblage (chalcopyrite, pyrite, small amounts of sphalerite). Inclusion of bornite in pyrite is also common in these deposits. 

The flotation of sphalerite, the sulfidic mineral source of zinc, is next considered as an example to illustrate the role of activators. This mineral is not satisfactorily floated solely by the addition of the xanthate collector. This is due to the fact that the collector products formed, such as zinc xanthate, are soluble in water, and so do not furnish a hydrophobic film around the mineral particles. It is necessary to add copper sulfate which acts as an... 

The copper sulfide formed on the surface of the sphalerite mineral reacts readily with the xanthate, and forms insoluble copper xanthate, which makes the sphalerite surface hydro-phobic. Such a reaction for activating sphalerite occurs whenever the activating ions are present in the solution. It is thus necessary to deactivate sphalerite (to prevent the occurrence of natural activation) in the case of some ores. With lead-zinc ores, for example, natural activation occurs due to Pb2+ in solution... 

From the perspective of ore genesis, these results seem disappointing in light of the fluid s high degree of supersaturation. Shanks and Bischoff (1977), for example, estimate that about 60 mg of sphalerite alone precipitate from each kg of ore fluid feeding the Atlantis II deep. The reaction to form chalcocite,... 

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