JpGU-AGU Joint Meeting 2017

講演情報

[EE]Eveningポスター発表

セッション記号 S (固体地球科学) » S-IT 地球内部科学・地球惑星テクトニクス

[S-IT27] [EE] Carbon in Planetary Interiors

2017年5月23日(火) 17:15 〜 18:30 ポスター会場 (国際展示場 7ホール)

[SIT27-P03] Pressure-induced phase transitions of vaterite, a metastable phase of CaCO3

*鍵 裕之1丸山 浩司1小松 一生1吉野 徹3中野 智志2 (1.東京大学大学院理学系研究科附属地殻化学実験施設、2.物質材料研究機構、3.東京都産業技術研究センター)

キーワード:vaterite, calcium carbonate, high pressure, phase transformation

Calcium carbonate plays an important role in global carbon cycle. Calcium carbonate has three polymorphs, calcite, aragonite and vaterite. Vaterite is a meta stable phase and no systematic experiments on the behavior under high pressure have been condcuted so far. In this study, pressure-induced phase transitions of vaterite, a metastable phase of CaCO3, were observed from Raman spectra and X-ray diffraction patterns at high pressure using diamond anvil cells at room temperature. Pressure dependence of Raman peaks assignable to the symmetric stretching vibration modes of carbonate ion indicated the phase transitions of vaterite. At 4.3 GPa, vaterite (vaterite I) transformed to a high-pressure form of vaterite (vaterite II). With increasing pressure, a part of vaterite II gradually transformed to calcite III, and the remainder of vaterite II transformed to another new phase (vaterite III). The phase transition from vaterite II to calcite III was irreversible, and calcite III back-transformed to calcite I during decompression. Moreover, at the pressures higher than 13.1 GPa, several diffraction spots were observed on an imaging plate, indicating another phase transition from vaterite III to a phase having coarse grains (vaterite IV). Our results indicate that vaterite undergoes more complex phase transitions at high pressure than other polymorphs of calcium carbonate, calcite and aragonite. These phase transitions of vaterite will open a window to understanding phase transitions of metastable minerals at high pressure.