Raman spectroscopy and XPS study of the thermal decomposition of Mg‐hornblende into augite

Abstract The breaking and reorganization of chemical bonds during the transformation of amphiboles to pyroxenes are obscure due to similar structures and seemingly stable tetrahedrons. A systematic heating experiment was carried out on amphibolites at medium and high temperatures (600–1180°C) to explore the transformation mechanism of double‐chain silicate minerals (amphiboles) to single‐chain silicate minerals (pyroxenes). It was found that the morphology of Mg‐hornblende changed significantly at 1050°C. Raman spectroscopy and X‐ray photoelectron spectroscopy (XPS) revealed that a large amount of electron transfer promoted H + escape during Fe 2+ oxidation to Fe 3+ . Meanwhile, the decrease of A Na, A K, and T Al shortens the distance between the two tetrahedrons and breaks the O‐Si‐O bond connecting the tetrahedron and octahedron M4. Electron transfer between the octahedral and tetrahedral sites occurs at approximately 600°C. At ~900°C, a part of the Ca‐O electrons was transferred to the Ca‐O‐Si. Finally, the O‐Si‐O bond break caused Ca in M4 to move into cavity A‐site to form augite together with Si‐O‐Si at the site of T1‐T1, which behaves accordingly, the number of electrons lost by Ca‐O is similar to that gained by Si‐O‐Si at 1050–1100°C. This study provides direct evidence of Raman spectroscopy and XPS to reveal the phase transformation mechanism and establish phase transition thermometers of amphiboles to pyroxenes.