R1: Characterization and description of minerals (Joint Session with The Gemmological Society of Japan)

[R1P-08] The higher hydrated analogue of zaccagnaite from the Ikuno mine, Hyogo Prefecture, Japan

*Masayuki Ohnishi¹, Norimasa Shimobayashi², Daisuke Nishio-Hamane³, Shoichi Kobayashi⁴, Takeshi Hisano⁵ (1. Non, 2. Sci., Kyoto Univ., 3. ISSP, Univ. of Tokyo, 4. Sci., Okayama Univ. of Sci., 5. Kwansei Gakuin Univ.)

Keywords:zaccagnaite, glaucocerinite, hydrotalcite supergroup, Ikuno mine

The higher hydrated analogue of zaccagnaite, ideally Zn₄Al₂(OH)₁₂[CO₃]·nH₂O (n > 3), from the Ikuno mine, Hyogo Prefecture, Japan. The mineral occurs as crusts of hexagonal platy crystals up to 80 μm across and 3 μm in thickness, in association with calcite and "limonite". It is pale blue to pale blue-green with pearly to vitreous luster. The mineral is space group R-3m, a = 3.058(2) and c = 32.63(9) Å. It can also be considered as the CO₃-dominant analogue of glaucocerinite.