Rate of Thermal Dehydration of Muscovite

By the use of an automatic thermogravimetric apparatus, weight loss versus time data were collected for muscovite at five different temperatures in the range 738° to 817°C. Initial sample weight rather than the external surface area was found to be a parameter of the rate of weight loss. A rate equation is presented that explains the observed logarithmic time dependence based on a model involving a systematic relief of strain during dehydration. These findings are supported by infrared spectra of muscovite in various stages of dehydration. It is also proposed that during dehydration aluminum ions in the octahedral layer shift from 6‐ to 4‐coordinated positions.