Neutron-diffraction structure of a low-water grossular at 20 K

G. A. Lager
Department of Geology
  University of Louisville, Louisville, Kentucky 40292, USA

G. R. Rossman
Division of Geological and Planetary Sciences
California Institute of Technology, Pasadena, CA  91125, USA

F. J. Rotella
IPNS Division, Argonne National Laboratory
Argonne, Illinois 60439, USA

A.J. Schultz
Chemistry and Materials Science Divisions
Argonne National Laboratory
Argonne, Illinois 60439, USA


The crystal structure of a low-water (0.16 wt% OH) grossular has been refined at 20 K by single-crystal time-of-flight neutron-diffraction methods. Comparisons with the room-temperature structure indicate that between 298 and 20 K, the silicate te trahedron undergoes a small rigid-body rotation that results in an increase in the y parameter of oxygen. The mechanism of thermal expansion is significantly different from that at high temperture where the tetrahedra do not rotate and changes in the structure reflect only unit-cell expansion.

The Crystal

The crystal before fabrication

IR of Ramana Grossular

Infrared spectrum in the OH region of the grossular from Ramona, California, normalized to 0.10 mm thickness

The IR data (text file)