Note on rock-forming minerals in the Joetsu district, Niigata Prefecture, Japan (7) Phillipsite from Yoneyama

概要

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Phillipsite occurs in amygdule and the cavities of basalt at Tanne, Yoneyama district, Niigata Prefecture, Japan. The phillipsite from Yoneyama is poor in Na content and rich in Ca content, as compared with phillipsite from sea bottom sediments and saline lake deposits. It has the low Si/Al ratio. The K/K+Ca ratio is about 0.5. The chemical composition of phillipsite is similar to phillipsites from volcanic rocks. The phillipsite does not form by reaction of glass in basalt and sea water. The formula of phillipsite was given as (K_<1.77>Na_<0.19> Ca_<1.81>Fe_<0.01>Al_<0.04>)_<3.82>(Al_<5.73>Si_<10.27>)_<16>O_<32>, 12H_2O. Unit-cell dimensions of the phillipsite are a = 9.880(3) Å, b = 14.244(4)Å, c = 8.663(2)Å, β= 124.38(8)^○ and V= 1006.2(4)Å^3.
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