NMR Spectroscopy of Inorganic Earth Materials

Abstract

Nuclear Magnetic Resonance (NMR) methods are now widely used for studying the structure and dynamics of solid, inorganic materials, including those central to the Earth sciences, as well as silicate melts and aqueous solutions. Spectra of minerals (as conveniently large single crystals) were collected soon after NMR was developed in the late 1940’s, and were instrumental in early refinements of the theory of NMR interactions in solids (Pound 1950; Petch et al. 1953). NMR on single crystals also provided important insights into issues such as symmetry distortion and phase transitions in minerals (Brun and Hafner 1962; Ghose 1964; Ghose and Tsang 1973). The critical, resolution-enhancing method of “magic-angle sample spinning” (MAS) was invented in the late 1950’s and demonstrated on NaCl (Andrew et al. 1959). However, it was not until the development of relatively high-field (e.g., 4.7 Tesla and above) superconducting magnets, and pulsed, Fourier-transform methods (requiring fast micro-computers) in the late 1970’s and early 1980’s that high-resolution NMR spectroscopy on nuclides such as 29Si and 27Al routinely started providing new structural information on minerals and glasses (Lippmaa et al. 1980; Smith et al. 1983; Magi et al. 1984). Technological advances continue to push the development of new applications of high resolution, solid-state NMR, for example magnets with fields of 21 T and even higher, MAS probes with spinning rates above 100 kHz (6 million revolutions per minute), and capabilities to observe high-quality spectra of ever-smaller samples (e.g., <1 mg). Probably more than any other commonly-applied spectroscopic methodology, NMR includes a wide array of techniques that allow the complex, and time-dependent, manipulation of the system under observation, in this case the nuclear spins of isotopes of many different elements. A rich variety of information about short-range (first and second atom neighbor distributions) and …