Powder diffraction patterns of samples annealed at different temperatures (see Table 1). The main characteristic peaks of minerals formed are shown in the top pattern. Below 973 K only forsterite peaks are observed. Above this temperature both ortho- and clinoenstatite form readily. Cristobalite and protoenstatite are recovered in samples quenched from 1378 K only. Indexation of the patterns was done using the software EVA (Bruker-AXS) and the database edited by the International Centre for Diffraction Data (ICDD).