Abstract
Electronic paramagnetic resonance (EPR) spectra of trace quantities of Mn+2 in solid solution in 
, 
, 
, 
, and 
are given. The utility of EPR in following phase changes is demonstrated. The transition from 
to 
is established as occurring within the temperature range, 1171°–1179°. The results of hydrothermal experiments indicate that 
is a metastable phase. It is established by EPR that the amorphous gel formed as an intermediate in the dehydration‐recrystallization of 
is in dynamic equilibrium with the solution phase.