Serpentine minerals discrimination by thermal analysis

This paper reports a complete set of TG, DTG, and DTA data, coupled with emitted gas analysis, for well-constrained, almost pure serpentine samples. Serpentine dehydroxylation takes place between 550 and 800 degrees C, with DTG and DTA peak temperatures progressively decreasing from antigorite (720 and 715 degrees C, respectively) to lizardite (708 and 714 degrees C), polygonal serpentine (685 and 691 degrees C), and chrysotile (650 and 654 degrees C). Antigorite has an additional diagnostic signal at similar to 740-760 degrees C, always absent in the other serpentines, and dependent on antigorite superperiodicity (T shift of similar to 20 degrees C from 36 to 49 angstrom modulation wavelength). A sharp exothermic peak occurs at extremely constant temperatures (similar to 820 degrees C), independently from the starting serpentine structure. The high-T mineral assemblage is always represented by forsterite and enstatite. Based on the observed relationships between serpentine structures and DTG/DTA dehydroxylation temperatures, thermal analysis may represent a useful tool for serpentine identification, particularly in the case of natural massive samples where different varieties are mutually intermixed. The accurate definition of serpentine mineralogy would have obvious implications in both geological-petrological and health-related issues.