[B-CG06] Rock-Bio Interactions and its Applications

[BCG06-P06] Revealing the black component on the eggshell of "black eggs" from Owakudani, Hakone Hot Springs, Japan

Rintaro Kimura¹, Kazutaka Mannen², Hidenori Kumagai³, Yohei Matsui³, Motoko Igisu³, *Yoshinori Takano³ (1.Hiroo Gakuen Junior and Senior High School, 2.Hot Springs Research Institute of Kanagawa Prefecture, 3.Japan Agency for Marine-Earth Science and Technology (JAMSTEC))

Keywords:Owakudani, Hakone Hot Springs, Black egg, The black component, Chemical analysis, Organic molecular analysis

Black egg or “Kuro-Tamago”, is a well-known souvenir of Owakudani fumarole area in Hakone volcano, Japan. The eggs, which were originally ordinary chicken eggs boiled in a certain natural hot water pond in the area, literally have black surface, which formed by some hydrothermal chemical reaction of the hot water in the pond. However, its black component has not yet been revealed, although it has been explained as iron sulfide formed on the surface of the egg shell. The black color on the surface eventually altered to a brownish color when left to stand within days scale. The observed phenomena would be problematic for the explanation so far, since iron sulfide is relatively stable in the atmospheric air. In this study, we successfully isolated the exterior black film material covering the egg shell in the solid state by immersing citric acid solution. We conducted various chemical analysis on the black film material and determined significant amount of carbon (C), nitrogen (N) and sulfur (S) together with protein-like substances, while no significant iron sulfide was indicated. Given the high carbon and nitrogen contents with biogenic amino acids and fatty acids, the black component may have been produced by the Maillard reaction in the hydrothermal environment. The high sulfur content also suggests the formation of high molecular weight organic polymers by sulfur-mediated cross-linking reactions. It was considered that the black egg as a well-preserved polymeric bonded organic substance.