Olivine group

Garnet Positions of absorption bands (cm-1) 0 (cm 1) CFSE (cm 1) CFSE (kJ/g.ion) Sources of data 

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Matsui Y. and Syono Y. (1968). Unit cell dimension of some synthetic olivine group solid solutions. Geochem. Jour, 2 51-59. 

Sumino Y. (1979). The elastic constants of Mn2Si04, Fe2Si04 and C02SiO4, and the elastic properties of olivine group minerals at high temperatnre. J. Rhys. Earth, 27 209-238. 

Nesosilicates are the simplest silicates. They contain isolated or independent Si04 tetrahedra. This group has also been called the orthosilicates. A secondary classification, the nesosubsilicates has been designated by Strunz (1957), who was the originator of the silicate classification. This subclass included species having a second anion or anionic radical. The nesosilicates include the gem minerals zircon, topaz, and the garnet and olivine groups. 

That solids with different compositions can adopt identical crystal shapes was documented in 1819 by Mitscherlich, who called the phenomenon isomorphism (Mitscherlich 1819, Melhado 1980). Isomorphism can describe phases with similar atomic architectures but unlike constituents, such as NaCl and PbS, and it also can refer to members of a continuous solid solution series, such as the olivine group with formula (Mg,Fe)2Si04. Three years later, Mitscherlich documented the complementary property of polymorphism, whereby phases with identical compositions occur as different structures (Mitscherlich 1822). Although mineralogists of the nineteenth century recognized the important inter-relationship between crystal structure and composition, the crystallographic probes available for structure determination did not keep pace with advances in wet chemical analysis. Consequently, understanding the effects that chemical modifications exert on crystal structures could be revealed only by careful measurements of subtle variations in habit. 

Other members of the olivine group have the same structure, but with Mg2+ ions partly or wholly replaced by Fe2+ or Mn2+. In olivine itself about io per cent of the Mg2+ ions of forsterite are replaced by Fe2+ fayalite and tephroite have the idealized compositions Fe2Si04 and Mn2Si04, respectively. 

Fayalite The Fe-rich olivine group endmember mineral with the formula Fe2Si04. 

Olivine. In the olivine group of minerals (important orthorhombic silicates), the energies of the [100], [010], and [001] dislocations are all different. In fact, the energy of the [010] dislocation will be much greater since it has a much larger Burgers vector. 

Forsterite is a mineral of the olivine group, which possess orthorhombic symmetry and a structure consisting of independent Si04 tetrahedra linked by divalent atoms... 

Losey A, Rakovan J, Huges J, Francis CA, Dyar MD (2004) Structural variation in the lithiophilite-triphylite scaies and other olivine-group structures. Canad Mineral 42 1105-1108... 

K2S04-type oxynitrides. From a crystallographical point of view, silicate minerals of the olivine group, sometimes called hexagonal spinels , and compounds crystallizing with the I3-K2SO4 type structure can easily be confused due to similarities... 

The end members of the olivine group, the structure of which consists of individual Si04 tetrahedra linked by divalent ions in sixfold coordination, are forsterite (Mg2Si04) and fayalite (Fe2Si04). Those commonly found in soils are usually intermediate in composition and partially altered because of the ease with which olivine weathers. The structure is orthohombic. 

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