Direct evidence of Lowenstein's rule violation in swelling high-charge micas

Abstract

The structure of high-charged micas, Na-n-micas (n = 2 and 4), a family of synthetic silicates with a wide range of applications, was investigated through the use of ¹⁷O solid-state NMR at natural abundance in order to preserve quantitative spectral information. The use of a very high-field and highly sensitive probehead, together with ¹⁷O NMR literature data allowed for the detection of an isolated signal at 26 ppm, assigned partially to AlOAl, as evidence of the violation of Lowenstein's rule for Na-4-mica.