Scope of crystal field theory

The major focus of the book is on mineral crystal structures that provide an ordered array of anions forming coordination polyhedra around the central cations. The thermodynamic data underlying many of the geochemical applications described in the first ten chapters are derived from energies of absorption bands in the optical spectra of minerals, which are most simply explained by crystal field theory. Use of experimentally determined energy level data rather than energy separations computed in molecular orbital diagrams is the emphasis of these early chapters. 

However, in sulphides and related minerals, the effects of covalent bonding predominate and orbital overlap must be taken into account. Thus, concepts of molecular orbital theory are described in chapter 11 and applied to aspects of the sulfide mineralogy of transition elements. Examples of computed energy diagrams for molecular clusters are also presented in chapter 11. There, it is noted that the fundamental 3d orbital energy splitting parameter of crystal field theory, A, receives a similar interpretation in the molecular orbital theory. 

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