Heat treatment of basalt-related sapphire from Binh Thuan deposit, Southern Vietnam

Yuparat KWANGSAWAT; Thitiphan ASSAWINCHAROENKIJ; Doan Thi  ANH VU; Waratchanok  SUWANMANEE; Chakkaphan SUTTHIRAT

doi:10.55713/jmmm.v36i4.2609

Authors

Yuparat KWANGSAWAT Department of geology, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand
Thitiphan ASSAWINCHAROENKIJ Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand ; Center of Excellence in Applied Mineral and Petrology Research Unit (AMP RU), Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand
Doan Thi ANH VU Saigon Institute of Gemstone Jewelry Artcraft, Hochiminh city, 008428, Vietnam
Waratchanok SUWANMANEE Institut für Mineralogie und Kristallographie, Universität Wien, 1090 Wien, Austria
Chakkaphan SUTTHIRAT Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand

DOI:

https://doi.org/10.55713/jmmm.v36i4.2609

Keywords:

Heat treatment, Corundum, Basaltic sapphire, Southern Vietnam, Beryllium-assisted heating

Abstract

Characteristics of basalt-related sapphires from Binh Thuan in Southern Vietnam were investigated before and after heat treatment. Heating at 700℃ to 1000℃, caused blue hue to fade noticeably, while blue color was intensified when heated at 1650℃. Subsequently, these sapphire samples were subjected to beryllium (Be)-assisted heating by a local professional gem treater, which yielded yellow to yellowish-blue hues. Absorption spectra of blue sapphires indicated absorptions at 378 nm, 387 nm, 450 nm, 580 nm, and 880 nm. However, yellow sapphires, after Be-assisted heating, did not exhibit absorptions at 580 nm and 880 nm. In the FTIR spectra, bands associated with OH stretching disappeared after being heated to 1650℃ as well as Be-assisted heating. Based on LA-ICP-MS analyses, an increase in Be concentration (5 ppma to 146 ppma) was detected following Be-assisted heating, which conclusively induces yellow coloration in sapphire.

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