Goldschmidt’s rule

New experimental data have modified Goldschmidt s rules. Thus, the CaO-NiO solution has been prepared by laser heating and subsequent deposition on a substrate of single-crystalline MgO [100]. The solid solution Mgi/3Fe2/30 was prepared by shockcompression of the mixture MgCOs +Fe[101].TheMgi xFexS solutions were... 

Numerous exceptions to Goldschmidt s rules have been found and it has been necessary to modify them, since it is not the ion size alone that determines if a metal ion occupies place in the growing crystal. 

In this case, however, the ISi jO component is at infinite dilution in a host of essentially pure YSi cO. Now we assume that Goldschmidt s first rule applies, i.e., we assume that if I and Y " " had exactly the same ionic radius then the standard free energy changes of reactions (1) and (4) would be the same. The actual difference between the standard free energy changes is assumed to be due to the work done in straining crystal and melt by introducing a cation which is not the same size as the site. This is a reasonable assumption for closed-shell ions such as Ca, Sr, and Mg " " and it also appears to work in those cases, such as the lanthanides, where crystal field effects are small (Blundy and Wood, 1994). For first row transition ions such as Co, and Cu, however,... 

In 1922 Assar Hadding at the Swedish University in Lund began to use X-ray analysis to determine the composition of minerals. Goldschmidt also rapidly apphed the new technique of X-ray fluorescence analysis and confirmed that Harlan s rule is also vahd for rare elements. 

This theoretical result is completely substantiated by experiment. Goldschmidt,31 from a study of crystal structure data, observed that the radius ratio is large for fluorite type crystals, and small for those of the rutile type, and concluded as an empirical rule that this ratio is the determining factor in the choice between these structures. Using Wasastjerna s radii he decided on 0.67 as the transition ratio. He also stated that this can be explained as due to anion contact for a radius ratio smaller than about 0.74. With our radii we are able to show an even more satisfactory verification of the theoretical limit. In Table XVII are given values of the radius ratio for a large number of compounds. It is seen that the max-... 

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