R1: Characterization and description of minerals

[R1P-10] Occurrence of holtstamite hydrogarnet from the Sekkaizawa and its high-pressure behavior

*Daisuke Nishio-Hamane¹, Koichi Momma², Akira Harada (1. ISSP, Tokyo Univ., 2. Nat’l. Mus. Nat. Sci.)

Keywords:Holtstamite, Hydrogarnet, Sekkaizawa, Chichibu mine, High Pressure

The most garnets are predominantly isometric cubic, while two hydrogarnets (holtstamite and henritermierite) have tetragonal symmetry without altering topology. The hydrogarnet can be written as Ca₃Al₂(SiO₄)_3-x(H₄O₄)_x, where x = 1 correspond to the end-member formula of holtstamite. To date, holtstamite is extermely rare mineral only occured from the Wessels mine, we showed that it exists as a large rock from the Chichibu Mine. High pressure study was also demostrated using this holtstamite.