DEHYDRATION PROCESSES OF GYROLITE

The thermal decomposition processes of natural and synthesized gyrolit e, which have a sheet silicate anion structure with Ca/Si molar ratio of 0.66, were compared mainly by Si-29 MAS NMR. In the two samples, th e silicate anions has the same structure (protonated Q3), however thei r crystallinity was different. The protonated Qs structure in both sam ples decomposed gradually below 800-degrees-C to form nonprotonated mo nomer (Q0) and chain silicate (Q1 and Q2). Above 900-degrees-C, the na tural gyrolite decomposed to pseudo-wollastonite and silica glass, whi le the synthesized one changed to pseudo-wollastonite and cristobalite via wollastonite. These differences are believed to be caused by the differences in their crystallinity, decomposition rate and the flux ef fect resulting from the glassification of the impurities.