Na-rich Garronite from Hirado-jima Island, Nagasaki Prefecture, Japan

Abstract

Na-rich garronite was found in basaltic rock with epistilbite and chabazite-Ca in Hirado Island. Ideal chemical formula of the garronite is shown as NaCa_2.5(Al₆Si₁₀)O₃₂ 14H₂O. Though the Na/(Na+Ca) molar of garronite generally is shown a range of 0.05 to 0.37, the Na-rich garronite is 0.49 to 0.60. The unit cell parameters, a=9.975(7) Ǻ, b=10.178(1), c=9.945(2), beta=89.977(1)° and V=1009.6(7)Ǻ³, are slightly larger in a axis, and smaller in c axis than those of garronite from Oki Island.