17:15 〜 18:45
[BCG07-P02] マグネシウムシリケートハイドレートの変質挙動: XANES法の適用
Sample analyses of the carbonaceous asteroid Ryugu collected by the Japanese spacecraft Hayabusa2 revealed that the majority of the samples are hydrous Mg silicates that formed by the aqueous alteration that once occurred in the Ryugu parent body (Ito et al 2022Nature Astronomy, Nakamura, et al 2023 Science). It is expected that the hydrous Mg-silicates formed in the Ryugu parent body record information on the water environment during the water alteration, and studies to clarify their mineralogical characteristics in detail have been conducted. In this context, Fujiya et al, (2024JpGU meeting) compared Mg K- edge X-ray Absorption Near Edge Structure (Mg-XANES) spectra of Ryugu samples with those of terrestrial reference materials. They found that most of the hydrous Mg silicates are Magnesium Silicate Hydrate (MSH) which is precursors of crystalline Mg layered silicates. On the other hand, the question remains as to why MSH, which is inherently unstable, persists after a geological time-scale event of the aqueous alteration.
MSH is a metastable phase formed at low temperatures and under alkaline conditions. MSH therefore transforms to talc and stevensite (or saponite if Al is included) at low Mg/Si molar ratios and to serpentine at high Mg/Si molar ratios (Nied et al, 2016Cem. Concr. Res.), MSH exhibits low crystallinity, making it difficult to trace the initial alteration process in detail based on powder X-ray diffraction (XRD), which is commonly used for mineral identification and characterization. Inoue et al, (2023Appl. Clay Sci.) showed that Mg-XANES, which provides information on the coordination environment of elements, can clarify the differences between MSH and other clay minerals. The purpose of this study is to quantitively reveal the transformation process of MSH to clay minerals using Mg-XANES measurement.
MSH is a metastable phase formed at low temperatures and under alkaline conditions. MSH therefore transforms to talc and stevensite (or saponite if Al is included) at low Mg/Si molar ratios and to serpentine at high Mg/Si molar ratios (Nied et al, 2016Cem. Concr. Res.), MSH exhibits low crystallinity, making it difficult to trace the initial alteration process in detail based on powder X-ray diffraction (XRD), which is commonly used for mineral identification and characterization. Inoue et al, (2023Appl. Clay Sci.) showed that Mg-XANES, which provides information on the coordination environment of elements, can clarify the differences between MSH and other clay minerals. The purpose of this study is to quantitively reveal the transformation process of MSH to clay minerals using Mg-XANES measurement.