Oxidation processes and thermal stability of actinolite

Abstract Understanding the thermal behaviour of iron-containing amphiboles (AB 2 C 5 T 8 O 22 W , = M (1) (2) (3)) at atomic-level scale may have important implications in several fields, including metamorphic petrology, geophysics, and environmental sciences. Here, thermally induced oxidation decomposition actinolite are studied by situ high-temperature Raman spectroscopy complementary thermogravimetric/mass-spectrometry analyses as well X-ray diffraction products amphibole decomposition. The effect Fe 2+ on dehydrogenation/dehydroxylation is followed comparing results with those for tremolite. We show that mobile charge carriers, namely polarons (conduction electrons coupled to FeO 6 phonons) H + cations, exist elevated temperatures ~ 1150–1250 K. temperature-induced breakdown a multistep process, involving (i) delocalization e ? from hydroxyl groups shared Fe-containing (3) species, which, however, remain crystal bulk; (ii) dehydrogenation ejection between 1250 1350 K, where can be considered “oxo-actinolite”, also next (1,3) (MgMgMg) configurations become delocalized mostly (iii) complete dehydroxylation consequent structure collapse above forming an 3+ -bearing defect-rich augitic pyroxene. tremolite occurs 1400 triggering immediately disintegration silicate double-chain into single SiO 4 -chains rearrangement octahedral strips B Ca cations pyroxene-type sheets 1450 result single-phase clinopyroxene intermediate composition diopside–clinoenstatite join.