R4: Mineral sciences of the Earth surface

[R4-10] Variation of aragonite axial ratios induced by Na substitution

*Taiga Okumura¹, Michio Suzuki², Toshihiro Kogure¹ (1. Univ. Tokyo Sci., 2. Univ. Tokyo Agric. Life Sci.)

Keywords:Aragonite, Sodium, Lattice constant, Axial ratio, Synthetic experiment

Some biogenic aragonites possess larger axial ratios (a/b and c/b) than abiotic counterparts. To verify the hypothesis that Na⁺ incorporation alters the axial ratios of aragonite, we synthesized aragonites in vitro in the presence of Na⁺. The axial ratios of synthetic aragonites became larger with higher Na content. The axial ratios decreased by heating at 250°C probably by the diffusion and segregation of Na⁺ from the crystal lattice of aragonite.