Gatta G D , Angel R J , American Mineralogist , 92 (2007) p.1446-1455, Elastic behavior and pressure-induced structural evolution of nepheline:, Implications for the nature of the modulated superstructure, Locality: intrusive aplite of Snipe River, Tambani, Nyasaland, Malawi, Sample: P = .0001 GPa, in air after decompression