Water and hydrogen release from perlites and opal

Abstract

The dehydration of two specimens of perlite from Palhaza (Hungary) and from Borovitza (Bulgaria) along with a specimen of Australian precious opal has been investigated by temperature controlled high-vacuum degassing experiments (DEGAS). Dehydration results in the loss of water over a wide range of temperatures due to the presence of both molecular and bound (silanol, Si–OH) water. A surprising observation is that hydrogen (H2) is also released. The hydrogen is observed to be released from both perlites and opal and both by diffusional processes and through the sudden explosive, bursting of inclusions which produce sharp spikes in the MS data. The origin of the hydrogen cannot be explained by a simple statistical distribution of the silanol species in the vitreous matrix; rather, it is more likely to be associated with an inverse-micellar decomposition of silanol species. Alternate sources of hydrogen such as meteoric waters or specific genetic origins based on the perlite or opal location and formation are discounted as the hydrogen release is found to be independent of CO2 and SO2 evolution.