Linn Nyi Myat Khine, Mandal Manik, Li Baosheng, Fei Yingwei, Landskron Kai
Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States.
Mineral Physics Institute, Stony Brook University, Stony Brook, New York 11794, United States.
ACS Omega. 2018 Oct 26;3(10):14225-14228. doi: 10.1021/acsomega.8b00484. eCollection 2018 Oct 31.
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 NaCO, 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.
在传统高压釜系统中，以1摩尔/升的氢氧化钠、0.8摩尔/升的碳酸钠和纯水作为矿化剂，进行了旨在实现近常压和常温下钛铁矿晶体生长的水热实验。结果发现，在所有矿化剂中，钛铁矿和柯石英的水热亚稳定性与热亚稳定性有很大不同，正因如此，无法生长出晶体。虽然钛铁矿和柯石英分别在高达500℃和高于1000℃时具有热稳定性，但它们的水热亚稳定性分别低于150℃和200℃。钛铁矿和柯石英的热致转变会产生非晶态产物，而水热致转变则会产生结晶石英。钛铁矿和柯石英都是自然界中存在的矿物，它们可能会暴露在水热条件下。这些相的低水热稳定性可能是解释这些矿物在自然界中稀少的一个重要因素。
