Fluoronyboite from Jianchang (Su-Lu, China) and nyboite from Nybo (Nordfjord, Norway): a petrological and crystal-chemical comparison of these two high-pressure amphiboles

摘要

Fluoronyböite, ideally NaNa₂(Al₂Mg₃)(Si₇Al)O₂₂F₂, has been found in the Jianchang eclogite pod, Su-Lu coesite-eclogite province, China. It has been approved as a new mineral by the IMA. Single-crystal structure refinement and electron microprobe analysis were used for characterization: C2/m, with a = 9.666(4), b = 17.799(6), c = 5.311(2) Å, ß = 104.10(3)°, V = 886.2(8) Å3, Z = 2, formula: A(Na_0.78K_0.06) _0.84 B(Na_1.53Ca_0.47) _2.00 C(Fe2+_0.89Mg_2.55Mn_0.01Zn_0.01Fe_0.323+Al_1.21Ti_0.01) _5.00 T(Si_7.14A_l0.86) _8.00O₂₂X(OH_0.84F_1.16) _2.00.