THE THERMAL-REACTIONS OF TALC STUDIED BY SI-29 AND MG-25 MAS NMR

Solid-state Si-29 and Mg-25 MAS NMR spectroscopy, in conjunction with thermal analysis and X-ray powder diffractometry, indicates that the t hermal decomposition of talc is an essentially simple reaction in whic h the loss of structural water is concomitant with the atomic rearrang ements involved in the formation of orthoenstatite with silica separat ion. The Mg-25 MAS NMR spectra of talc, enstatite and partially conver ted materials suggest no major differences in the octahedral cation en vironments of these phases, and provide no evidence for the incorporat ion of Mg into the amorphous silica phase. Neither the Si-29 nor the M g-25 spectra indicate the formation of a reaction intermediate such as a pyribole, which, if formed, may however have characteristics which are too similar to the talc and pyroxene units from which it is compos ed to be distinguished by NMR.