南薩型珪化岩鉱床に伴うスドーアイトとトスダイト

抄録

Sudoite and tosudite were found in hydrothermal alteration aureole of Nansatsu-type silicified rock deposit in the Makurazaki area, Kagoshima Prefecture, Japan. The d (060) values of the sudoite and tosudite are 1.508 and 1.506 Å, respectively.The structural formula of the sudoite is (Al_2.08 Mg_2.56 Fe³⁺_0.40Ti_0.06 Li_0.02 K_0.04 Na_0.02)(OH) ₁₂ Al_4.00 (Si_7.08 Al_0.92) O₂₀ (OH) ₄, and that of the tosudite is (Al_1.26 Mg_1.60 Fe³⁺_0.11Ti_0.01 Li_0.01 Mn_0.01 K_0.17 Na_0.03)(OH) ₆ Al_4.00 (Si_6.46 Al_.54) O₂₀ (OH) ₄.These specimens are characterized by relatively large amounts of Mg and very small amounts of Li. The basal spacing of tosudite is 29.77 Å under 50% relative humidity, and it changed to 31.37 Å after ethylene glycol solvation and to 23.74 Å after heating at 500°C for 1 hr. The basal spacing of Mg-saturated tosudite sample expanded to 31.41 and 32.17Å after ethylene glycol and glycerol solvation, respectively. However, K-saturated sample showed resistivity against the expansion by these treatments. Based on statistic analysis of chemical composition, a positive relationship was recognized between the number of tetrahedral Al and that of octahedral Mg. The result suggests that the small expansion ability of K-saturated present tosudite sample may be attributable to higher negative charge of the tetrahedral sheets.