Amaterasuite, Sr₄Ti₆Si₄O₂₃(OH)Cl, a new mineral from jadeitite, a representative stone of Japan

Abstract

新鉱物・アマテラス石の発見 --日本の国石「ヒスイ」から見つかった新種の鉱物-- . 京都大学プレスリリース. 2025-08-07.Amaterasuite is a new mineral found in jadeitite, a representative stone of Japan, and was thus named after Amaterasu Omikami, one of the most important goddesses in Japanese mythology, as a tribute to Japanese stone culture. The new mineral was found in the Osayama mountain area, Osa-osakabe, Niimi City, Okayama Prefecture, Japan. Amaterasuite appears as bundles consisting of needle- to plate-shaped crystals as large as 150 µm around rutile. The Mohs hardness is 6. Its tenacity is brittle, and its calculated density is 4.0 g·cm⁻³. Under plane-polarized light, the mineral is pleochroic, changing from blue to brown. The empirical formula, calculated on the basis of 23 O + 2 (OH,Cl) atoms per formula unit, is (Sr₃.₃₂Ba₀.₆₄)Σ₃.₉₆(Ti₅.₇₃Fe₀.₁₆Nb₀.₀₂)Σ₅.₉₁Si₄.₁₅O₂₃(OH)₀.₉₅Cl₁.₀₅; thus, its ideal formula is Sr₄Ti₆Si₄O₂₃(OH)Cl. The unit-cell parameters refined by powder X-ray diffraction using 80 peaks with large d-values are a = 5.85558(2) Å, b = 20.43960(8) Å, c = 33.28240(12) Å, and V = 3983.43(3) ų (Z = 8) in the orthorhombic Fddd space group. The structure of amaterasuite from the metajadeitite area was fully identified as amaterasuite-4O, which is characterized by its dual nature, encapsulating two types (A and B) within a unit cell. The occupancy rates of the A and B types were estimated to be ∼ 85 and ∼ 15%, respectively. The refined site occupancies at the SrA and BaB sites indicate a strong site preference for Sr, similar to the preferential site occupancies in synthetic titanosilicate compounds