Dalyite (K₂ZrSi₆O₁₅) and Zektzerite (LiNaZrSi₆O₁₅) in Aegirine-bearing Albitite from Iwagi Islet, SW Japan

Abstract

 The rare potassium zirconium silicate dalyite and lithium sodium zirconium silicate zektzerite have been found in Cretaceous aegirine albitite from Iwagi Islet, Southwest Japan. Electron microprobe analyses of the dalyite and zektzerite yielded the following empirical formulas based on 15 oxygens: (K_1.93Ba_0.01)_Σ1.94(Zr_0.99Hf_0.02)_Σ1.01Si_5.98O₁₅ and Na_1.03(Zr_0.96Hf_0.02Y_0.01Sc_0.01)_Σ1.00Li_1.02(Si_5.95Al_0.04)_Σ5.99O₁₅, respectively. The occurrence of porous zircon, dalyite, and mantles of zektzerite on resorbed zircon in the albitite suggests that those zirconosilicate minerals are the products of metasomatic mineral replacement reactions by Na-, K-, and Li-rich hydrothermal fluids. This is the first documented occurrence of dalyite and zektzerite in the Japanese Islands.