Exploratory Study on the High-Temperature and High-Pressure Modification of Natural Jadeite Jade

This study used low-quality natural jadeite jade, whose principal mineral phase is jadeite, as the starting material, and carried out exploratory high-temperature and high-pressure modification experiments with a cubic-anvil press. Two processing routes were investigated: direct high-temperature/high-pressure treatment within the jadeite stability field, and a route involving melting-quenching in the low-pressure metastable region to prepare a glass precursor followed by crystallization in the high-pressure stability field. The effects of encapsulation material, pressure, temperature, and holding time on the formation and crystallization behavior of the NaAlSi₂O₆ glass precursor were systematically examined. The results show that the former route did not significantly improve the transparency or color uniformity of the samples, nor did it produce obvious densification of the microstructure. In contrast, in the latter route, high-quality transparent and bubble-free glass precursors were obtained without encapsulation and with Mo or Re encapsulation, among which the Re-encapsulated sample showed the best overall performance. For the Ta-encapsulated sample, the main phase after crystallization was NaTaO₃. Crystallization experiments using the Re-encapsulated glass precursor further indicate that higher temperature is more favorable for overall crystallization, while prolonged holding time promotes crystallization from the rim toward the interior and gradually leads to the formation of a fibrous interwoven microstructure. These results demonstrate that, compared with direct high-temperature/high-pressure treatment within the jadeite stability field, the route involving structural reconstruction through a glass precursor followed by high-pressure crystallization exhibits greater potential for modification.