Disordering of the cations between the T and M sites complicates the analysis of the vibrational spectra of the ${\mathrm{MgAl}}_2$${\mathrm{O}}_4$ spinel, as well as many other spinels; thus, the Raman spectrum of ${\mathrm{MgAl}}_2$${\mathrm{O}}_4$ has not been satisfactorily assigned. Raman spectra of a natural spinel are reported that demonstrate the effect of rapid disordering of Mg and Al cations at high temperatures and the subsequent quenching of the disorder when the spinel was rapidly cooled to ambient temperature. These spectra are interpreted to resolve divergent interpretations of vibrational spectra of natural and synthetic ${\mathrm{MgAl}}_2$${\mathrm{O}}_4$ spinels.

• Received 18 September 1991

DOI:https://doi.org/10.1103/PhysRevB.45.500