The diffraction experiment in the study of solid solutions: Long-range properties
Published:January 01, 2001
This chapter provides a short review of results that have been obtained on the structure and chemistry of mineral solid solutions using diffraction methods. It is written to provide a simple, sometimes even colloquial, discussion of tie type of information, loosely termed long-range, that can be determined in the study of complex chemical/structural systems such as minerals. Different aspects will be illustrated through the extensive crystal-chemical studies made at the CNR-CSCC in Pavia, Italy, combining X-ray single-crystal structure refinements with in situ electron-microprobe and ion-microprobe analysis. The same general approach can be applied to structural data obtained by other long-range techniques (e.g., powder diffraction and neutron and electron scattering measurements).
For a review of the theory and the practical aspects relating to crystal-structure analysis, the reader is referred to the IUCr text Fundamentals of crystallography (edited by C. Giacovazzo, 1992). For questions related to refinement procedures, one can consult the review regarding difficult refinements by Watkin (1994) and the proper chapter of the International tables for crystallography (Albinati et al., 1992). The website of the IUCr (www.iucr.org) also provides a mine of useful information. Further references on crystallographic studies of solid solutions and more detailed discussion can be found in individual works or by use of search programs for the mineralogical literature.
The formation of a mineral solid solution results from the interplay between a chemically complex environment and the ability of many structures to incorporate different ions at the same structural site.
Figures & Tables
Solid Solutions in Silicate and Oxide Systems
The EMU book series or notes, as they are called, were introduced to provide university teachers with up-to-date reviews in important, rapidly evolving areas of mineralogy, petrology and geochemistry. They are also meant to introduce scientists into special and often interdisciplinary fields of research. In this regard, a volume on solid solutions is current and sorely needed. The solid Earth, as well as many meteorites and the other solid planets, consists for the most part of mineral solid solutions. Research on solid solutions is extremely broad encompassing work in physics and chemistry, metallurgy, materials science and, last but not least, mineralogy and petrology. Hence, because the theme is so strongly interdisciplinary in nature, the workshop was organised to include solid state physicists, physical chemists, crystallographers, mineralogists and petrologists. The various chapters reflect some of this diversity and show what mineralogy has become. Experimental investigations in mineralogy now routinely include different types of spectroscopies along with more traditional phase equilibrium, X-ray diffraction, calorimetry, and TEM methods. There have also been new and impressive developments in theory and computation. Many computational approaches relating to the study of solid solutions, for example, the Cluster Variation Method or Monte Carlo simulations, have been brought in from materials science, chemistry and physics. It can be concluded that the traditional or historical, and perhaps artificial, boundaries between the various disciplines are disappearing. Many current research efforts in mineralogy are similar to those in chemistry, materials science and physics.