Insights into the Hydrothermal Metastability of Stishovite and Coesite

Nyi Myat Khine Linn; Manik Mandal; Baosheng Li; Yingwei Fei; Kai Landskron

doi:10.1021/acsomega.8b00484

Insights into the Hydrothermal Metastability of Stishovite and Coesite

ACS Omega. 2018 Oct 26;3(10):14225-14228. doi: 10.1021/acsomega.8b00484. eCollection 2018 Oct 31.

Authors

Nyi Myat Khine Linn¹, Manik Mandal¹, Baosheng Li², Yingwei Fei³, Kai Landskron¹

Affiliations

¹ Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States.
² Mineral Physics Institute, Stony Brook University, Stony Brook, New York 11794, United States.
³ Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, United States.

Abstract

Hydrothermal experiments aiming at the crystal growth of stishovite near ambient pressure and temperature were performed in conventional autoclave systems using 1 M (molar) NaOH, 0.8 M Na₂CO₃, and pure water as a mineralizing agent. It was found that the hydrothermal metastability of stishovite and coesite is very different from the thermal metastability in all mineralizing agents and that because of this fact crystals could not be grown. While stishovite and coesite are thermally metastable up to 500 and >1000 °C, respectively, their hydrothermal metastability is below 150 and 200 °C, respectively. The thermally induced conversion of stishovite and coesite leads to amorphous products, whereas the hydrothermally induced conversion leads to crystalline quartz. Both stishovite and coesite are minerals occurring in nature where they can be exposed to hydrothermal conditions. The low hydrothermal stability of these phases may be an important factor to explain the rarity of these minerals in nature.