Iron oxide crystal structure

Description soils with abundant iron oxides crystallized but primary minerals not completely altered. Clay minerals with 1 1 structure. 

It has been known for a long time that two ciystalline solids, one which of starts at the surface of the other, often show mutual orientation relationships this is the process of epitaxy. Studies such as thin layers of oxides formed by oxidation of a metal, for example, have shown such a process. Figure 11.6 shows the example of the schematic orientations of cubic iron oxide (FeO) formed on the 001 side of the cubic iron. The side of the iron oxide cube is 2.86 A. The parameter of FeO is 4.29 A. In the isolated crystal, FeO iron atoms are spaced at 4.29 / VI = 3.89 A intervals, resulting in a slight deformation of the iron oxide crystal. If the layer of FeO is thick, the defect fades away from the interface the oxide has found its own structure. 

Analcite (NajOAljOj SiO I O), a cubic crystal structure, is formed at high temperatures. It is similar to acmite and also invariably is found beneath sludges of hydroxyapatite or serpentine or under porous deposits of iron oxides. 

A colorless mineral known as corundum (composed of aluminum oxide) is colorless. A red variety of corundum known as ruby, a precious stone, owes its color to impurities of chromium within the crystal structure of corundum. Blue and violet varieties of corundum are classified as sapphires, the blue being the result of iron and titanium impurities, and the violet of vanadium impurities within the corundum crystal structure. Another colorless mineral is beryl (composed of beryllium aluminum silicate) but blue aquamarine, green emerald, and pink morganite, are precious varieties of beryl including different impurities aquamarine includes iron, emerald chromium and vanadium, and morganite manganese. 

Chromium has a similar electron configuration to Cu, because both have an outer electronic orbit of 4s. Since Cr3+, the most stable form, has a similar ionic radius (0.64 A0) to Mg (0.65 A0), it is possible that Cr3+ could readily substitute for Mg in silicates. Chromium has a lower electronegativity (1.6) than Cu2+ (2.0) and Ni (1.8). It is assumed that when substitution in an ionic crystal is possible, the element having a lower electronegativity will be preferred because of its ability to form a more ionic bond (McBride, 1981). Since chromium has an ionic radius similar to trivalent Fe (0.65°A), it can also substitute for Fe3+ in iron oxides. This may explain the observations (Han and Banin, 1997, 1999 Han et al., 2001a, c) that the native Cr in arid soils is mostly and strongly bound in the clay mineral structure and iron oxides compared to other heavy metals studied. On the other hand, humic acids have a high affinity with Cr (III) similar to Cu (Adriano, 1986). The chromium in most soils probably occurs as Cr (III) (Adriano, 1986). The chromium (III) in soils, especially when bound to... 

Manganese nitrosyl porphyrins [215] are considered good models for the iron-nitric oxide analogs, which are relatively unstable but very vital to many biological operations. A six-coordinate manganese nitrosyl porphyrin of the form (por)Mn(NO)(L), where por can be TTP (TTP = tetra(4-methylphenyl)porphine) and L = piperidine, methanol, 1-methyhmidazole, has been prepared [216] in moderate yields by the reductive nitrosylation of the (por)MnCl complex with NO in piperidine. The crystal structures of these compounds give indication of a linear Mn-NO bond [215]. 

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