SI-29 MAS NMR RELAXATION STUDY OF SHOCKED COCONINO SANDSTONE FROM METEOR CRATER, ARIZONA

Si-29 nuclear magnetic resonance (NMR) spectroscopy was used to charac terize the silica phases in a moderately-shocked Coconino sandstone fr om Meteor Crater, Arizona. The spectra were recorded using direct pola rization, magic-angle spinning, and variable delay times in a saturati on recovery pulse sequence. Resonances observed at -97.3, -107.1, -113 .9 and -191.2 ppm were assigned to a densified hydrous form of amorpho us silica (D phase), quartz, coesite and stishovite phases, respective ly. The relative percentages were estimated as 1.7, 80.6. 16.4 and 1.3 % for the D, quartz, coesite, and stishovite phases. The power-law rec overies of the magnetization for the quartz and coesite phases can be interpreted in terms of their phase geometries.