宮城県仙台市三滝安山岩質玄武岩ジオード中の鉄サボナイト

抄録

Deep green saponites have been found in geode of andestic basalts from Sendai, Japan. The mineral has been confirmed by X-ray diffraction, D.T.A. and chemical analyses. Scanning electron microscopy shows them as small sphelurites. The structural formula of the mineral is given as
Ca_0.35(Mg_3.02Fe²⁺_3.03Ti_0.04Mn_0.04Al_0.01)(Si_6.89Al_1.11)O₂₀(OH)₄
The results show that the mineral is the richest in Fe in saponites descried up to data and Fe²⁺/Mg²⁺=1.003. It may be thought that the saponites grow rapidly on small nucleuse under hydrothermal condition, resulting in spherulites.