In-situ high-temperature behaviour and breakdown conditions of uvite at room pressure

Abstract

The thermal behaviour of an uvite from San Piero in Campo (Elba Island, Italy) was investigated at room pressure through in-situ High-Temperature X-Ray Powder Diffraction (HT-XRPD), until the breakdown conditions were reached. The variation of uvite structural parameters (unit-cell parameters and mean bond distances) was monitored together with site occupancies and we observed the thermally-induced Fe oxidation process counterbalanced by (OH)− deprotonation, which starts at 450°C and is completed at 650°C. The uvite breakdown reaction occurs between 800 and 900°C. The breakdown products were identified at room temperature by X-Ray Powder Diffraction (XRPD) and the breakdown reaction can be described by the following reaction: tourmaline → indialite + yuanfuliite + plagioclase + “boron-mullite” phase + hematite.

Compositional Variation and Crystal-Chemical Characterization of a Watermelon Variety of Tourmaline from Anjanabonoina, Central Madagascar

“…The presence of tourmalines in diagenetic zones and hydrothermal deposits suggests that the lower limit for the formation of these minerals is defined approximately at 150 • C and 100 MPa [2,3]. The upper thermal stability has been observed in high temperature experiments between 725 • C and 950 • C depending on the pressure and composition [4][5][6][7][8][9].…”