千葉県平久里産含バリウム tobermorite

概要

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Tobermorite from Heguri, Chiba Prefecture, occurs as veinlets cutting a basic tuff of Mineoka Group of Eocene age, suffering the metamorphism of zeolite facies. One of the most barium-rich analyses yields the empirical formula (Ca_<4.42>Ba_<0.08>(Na_2)_<0.05>(K_2)_<0.04>)_<Σ4.59>_(Si_<5.34>Al_<0.66>)_<Σ6.00>_O_<14.52>(OH)_<3.49>・3.20H_2O on the basis of Si+Al=6,specifying the material to be a barium-bearing aluminian tobermorite. The sharp X-ray powder diffraction pattern is explained by a C-centered orthorhombic cell with a 11.255,b 7.375,c 22.760 A, Z=4,though nearly all the diffracrions can be indexed by a subcell with a'=1/2a, b'=1/2b, and c'=c. The compositional variation of natural tobermorites is found to be approximately covered within the range from Ca_5Al_<0.5>Si_<5.5>O_<15.5>(OH)_<2.5>・4H_2O to Ca_4AlSi_5O_<13>(OH)_5・4H_2O, demonstrating a linear reciprocal relation between the total number of nontetrahedral cations and aluminum.
国立科学博物館の論文