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[SCG47-P15] Calcareous sinter from Shirahone hot spring area, Nagano Prefecture: Occurrence and color change
Keywords:Calcareous sinter, Shirahone hot spring, Transmission electron microscopic analysis
White and pale-yellow calcareous sinter, precipitated from the Shirahone hot spring area, Nagano Prefecture, is distributed around the gushing point. Its color changes to purple, light blue or reddish-purple over time.
In this study, the formation environment of the Shirahone calcareous sinter and the factors of the color change over time of the calcareous sinter were investigated. The changes of the collected samples were observed in three states: vacuum and open space conditions. For the observation of internal textures and identification of the constituent materials, field emission electron probe micro analysis, powder X-ray diffraction analysis and transmission electron microscopic analysis were performed.
The color of the sample stored in the vacuum condition was not changed, but the color of the sample in the open space of the room changed characteristically from white and pale yellow to purple, light blue and reddish purple. In the colored part of the surface of the calcareous sinter, fibrous substances with several µm in diameter and a hollow center are observed. The constituent elements of the fibrous substances are N, Na, Mg, Al, Si P, S, K, Ca and Cl. In addition, Mn and Fe were detected in the purple and reddish-purple parts of the fibrous substances: Fe content is high only in the dark purple part, and Fe, Mn and Ti in the light blue part. No powder X-ray reflections were given from the colored calcareous sinter diffraction analysis did not reveal any diffraction lines from the fibrous substances. On the other hand, transmission electron microscopy showed the presence of fine particles of a few nm in size, which might have been formed by the oxidation of transitional metal ions in the fibrous substances. Based on the occurrence and the constituent elements, the fibrous substances might be formed by biomineralization of microorganisms on the calcareous sinter surface.
The results of this study suggest that the change in color of the calcareous sinter is due to the incorporation of transition metal elements such as Fe and Mn as fine nanoparticles in the fibrous substances and their oxidation in the air.
In this study, the formation environment of the Shirahone calcareous sinter and the factors of the color change over time of the calcareous sinter were investigated. The changes of the collected samples were observed in three states: vacuum and open space conditions. For the observation of internal textures and identification of the constituent materials, field emission electron probe micro analysis, powder X-ray diffraction analysis and transmission electron microscopic analysis were performed.
The color of the sample stored in the vacuum condition was not changed, but the color of the sample in the open space of the room changed characteristically from white and pale yellow to purple, light blue and reddish purple. In the colored part of the surface of the calcareous sinter, fibrous substances with several µm in diameter and a hollow center are observed. The constituent elements of the fibrous substances are N, Na, Mg, Al, Si P, S, K, Ca and Cl. In addition, Mn and Fe were detected in the purple and reddish-purple parts of the fibrous substances: Fe content is high only in the dark purple part, and Fe, Mn and Ti in the light blue part. No powder X-ray reflections were given from the colored calcareous sinter diffraction analysis did not reveal any diffraction lines from the fibrous substances. On the other hand, transmission electron microscopy showed the presence of fine particles of a few nm in size, which might have been formed by the oxidation of transitional metal ions in the fibrous substances. Based on the occurrence and the constituent elements, the fibrous substances might be formed by biomineralization of microorganisms on the calcareous sinter surface.
The results of this study suggest that the change in color of the calcareous sinter is due to the incorporation of transition metal elements such as Fe and Mn as fine nanoparticles in the fibrous substances and their oxidation in the air.