²⁷Al NMR spectroscopy of minerals and related materials

We present a review of the applications of ²⁷Al NMR methods to investigations of the structures of minerals, primarily alumino-silicates, and related synthetic compounds. Such materials are ubiquitous in the earth and other terrestrial planets. Because of their diverse structures and compositions, they also provide examples of many situations in which ²⁷Al NMR spectroscopy can provide useful information. Thus, they serve well as model compounds for synthetic crystalline and amorphous materials and usefully illustrate the applications of many techniques. The advent of high-field superconducting magnets (H ₀>9 T) has made application of ²⁷Al NMR to solids much more effective than it was previously, and we focus primarily on these recent applications but also discuss older, single-crystal data. ²⁷Al NMR methods can be used for many purposes in investigations of solids. Here we emphasize the following. 1) Determination of the Al coordination number and the polymerization of tetrahedrally coordinated Al. 2) Determination of tetrahedral Al/octahedral Al ratios. 3) Investigation of tetrahedral Al, Si order/disorder in, especially, framework-structure alumino-silicate phases. 4) Investigation of the static structural changes and dynamical behavior of crystals undergoing structural phase transitions. 5) Investigation of the local symmetry of Al-sites through the quadrupole coupling constant and asymmetry parameter.