In this, the last major chapter of the book, we turn our attention to the applications of modern electronic structure models and concepts to more general geochemical problems; namely, those described by Goldschmidt as being concerned with the “distribution of elements in the geochemical spheres and the laws governing the distribution of the elements” (see Preface). The majority of minerals and rocks originally formed by crystallization from melts, and so the first section of this chapter is devoted to considering the nature of melts (and glasses), structure and bonding in melts, and the partitioning of elements (particularly transition elements) between the melt and crystallizing solid phases. The classic work of Bowen (1928) led to the recognition of particular sequences of crystallization and crystal-melt reaction relationships in the silicate melts from which major rock types form, as enshrined in the “Bowen Reaction Series.” Attempts were also made to explain the incorporation of particular elements into particular mineral structures using simple crystal chemical arguments, notably as laid down in “Goldschmidt’s Rules” (Goldschmidt, 1937). Such concepts are reappraised in the light of modern electronic structure theories. The other major realm of formation of minerals and rocks, and the most important medium of transport and redistribution of the chemical elements at the Earth’s surface, is the aqueous solution. The molecular and electronic structures of aqueous solutions, their behavior at elevated temperatures, formation and stabilities of complexes in solution, and the mechanisms of reactions in solution are all considered in the second section of this chapter. The surfaces of minerals (or other crystalline solids) differ from the bulk material in terms of both crystal structure and electronic structure. A great variety of spectroscopic, diffraction, scanning, and other techniques are now available to study the nature of solid surfaces, and models are being developed to interpret and explain the experimental data. These approaches are discussed with reference to a few examples of oxide and sulfide minerals. Although relatively few studies have been undertaken specifically of the surfaces of minerals, many of the reaction phenomena that occur in natural systems take place at mineral surfaces, so that such surface studies represent an important area of future research.
Does bacterial weathering play a significant role in rock weathering?