The mechanism of decomposition of serpentines from peridotites on heating

Serpentines from peridotites of San Jose and New Idria (California, USA) were previously heat treated ranging from 400 to 1,260 A degrees C, and then leached by using an original approach for acid processing of dehydrated serpentines. This approach is capable of releasing from the dehydrated serpentines ortho-[SiO4](4-), di-[Si2O7](6-), and other silicate anions, and moving them into solution in the form of soluble silicic acids. The discovery of these anions has led to the idea of the existence of differences in electronic configuration of Si-O bonds in siloxane bridges and different amount and allocation of ortho-[SiO4](4-) and meta- [(SiO3)(2-)](n) silicate anions in serpentines silicate layers thus providing a new deeper insight into the mechanism of the temperature-induced decomposition of the serpentine silicate structure. It should be emphasized that in spite of a great number of studies devoted to the temperature-induced dehydroxylation and recrystallization processes of serpentine minerals, the mechanism of serpentine decomposition is still poorly understood because no one has studied particularities of the structural organization of silicate layers in serpentines. The effect of thermal treatment at different temperatures ranging from 400 to 1,260 A degrees C for 2 h on the above mentioned serpentinite samples was characterized by thermal analysis, X-ray diffraction, and chemical analysis. The observed evidence made possible a comprehensive modeling of the relevant dehydroxylation, high-temperature crystallization, and recrystallization reactions. Complemented by chemical analysis data, the results obtained allows understanding the basic principles of the serpentine decomposition and crystallization processes, which govern the formation of stable high-temperature products like forsterite, enstatite, and protoenstatite, as well as the formation of different amount of silicic acids in solution via the new approach. These studies are of great interest and value to the pure and applied material sciences connected with serpentinites.