Summary: Standard heat treatments of 700° C for 3 hours, 1000° C for 1 hour. and 1300° C for 1 hour, both in a nitrogen atmosphere and in air, were applied to several samples of chevkinite and perrierite, and X-ray powder photographs were taken of the unheated and the heated materials.

Metamict chevkinites from the Urals, USSR, and from Ifasina, Madagascar, give the chevkinite phase when heated in nitrogen at 1000° C for 1 hour, but when heated in air at 1300° C for 1 hour give the perrierite phase. Perrierites only give the perrierite phase when heated in air or in nitrogen. A criterion for the identification of metamict samples of these two minerals was deduced from these experiments.