Orthoericssonite from the Hijikuzu mine, Iwate Prefecture, Japan

Abstract

Orthoericssonite, BaMn²⁺₂Fe³⁺ [O|OH|Si₂ O₇], hitherto reported only from the Långban mine, Sweden, was found in a jacobsite-bearing rhodonite-aegirine-tephroite ore from the Hijikuzu mine, Iwate Prefecture, as a product of strong thermal metamorphism due to granitic intrusion. It is orthorhombic, space group Pmmn, a₀=20.30Å, b₀=6.986Å, c₀=5.387Å, Z =4. Wet chemical analysis by K. N. gives the empirical formula (Ba_0.688Sr_0.256K_0.024Na_0.013Li_0.003)_0.984(Mn_1.435²⁺Fe_0.546²⁺Mg_0.086)_2.067(Fe_0.931³⁺Ti_0.093Al_0.034)_1.058Si_2.062 O_7.000(O_1.389(OH)_0.611)_2.000 as O=9, specifying it as a strontian and ferroan variety. It is optically biaxial positive, 2V about 50°, r ?? v strong, ns α=1.802, β=1.840, γ=1.888; strongly pleochroic, X=yellowish brown, Y=reddish brown, and Z=dark brown.