Ti- and Ba-rich tri-octahedral micas occur in fractionated basic igneous rocks, metasomatized mantle peridotites, metamorphosed pelites/carbonates, and hydrothermally altered mineral deposits. Electron microprobe analyses (EMP), with all iron reported as FeO, were widely used in the 1970/80s to interpret Ti and Ba substitution mechanisms, based on 22 O2– unit cell calculations, implying that cation vacancies occur in octahedral and/or intersheet sites. In 1996 EMP with chemical and physical analyses for ferric and total Fe, H2O, (OH), and element-specific Fe X-ray Absorption Spectroscopy (both K and L-edges) established valence states for Fe and Ti and cation site occupancies, that ∼50 % O replaces (OH) molecules, and that 24 anion cell formulae show the absence of cation vacancies. Cell formula calculation protocol for phlogopitic micas is refined here and results tested against the stoichiometric formula for vacancy-free phlogopite, XIIK2VIMg6IV[Si6Al2]O20(OH)4. Hypothetical sheet silicate compositions, calculated with fixed contents of vacancies linked to particular mixed-valence element substitutions, confirm that reliable unit cell formulae for natural mica solids require that each stoichiometric vacancy must be accounted for. If reliable estimates for ‘excess O’ (denoted WO2−) are assigned to EMP analyses, the proportion of the oxy-mica component in a mica solid solution can be defined. This approach is tested using published analyses for Ti- and Ba-rich biotites from fractionated basic and ultramafic volcanic igneous rocks (oxymica range 2.5–45 %; TiO2 up to 14 %; BaO up to 23 %), upper mantle peridotites (equivalent values 7–18 %; 6 %; 0.7 %), and metasomatised upper mantle (2–37 %; 9 %; 23 %). Enrichments of Ti and Ba in micas are clearly linked to the extra oxygen charge required to neutralise the more highly charged Ba2+ and Ti4+ replacing K+ and Mg2+.

中文翻译：

---

碱性碱性和上地幔火成岩中富含钛和钡的金云母云母;重新评估和合理化化学计量学、稳定性和 Fe 价估计


富含钛和钡的面体云母出现在分馏的碱性火成岩、交代化的地幔橄榄岩、变质的钙质岩/碳酸盐岩和热液蚀变的矿床中。电子显微探针分析 （EMP），所有铁都报告为 FeO，在 1970/80 年代被广泛用于解释 Ti 和 Ba 取代机制，基于 22 O2– 晶胞计算，这意味着阳离子空位发生在八面体和/或片间位点。1996 年，EMP 对铁和总铁、H2O、（OH） 以及元素特异性 Fe X 射线吸收光谱（K 和 L 边缘）进行了化学和物理分析，确定了 Fe 和 Ti 的价态以及阳离子位点的占据，即 ∼50 % O 取代 （OH） 分子，并且 24 个阴离子细胞公式显示没有阳离子空位。金云母的细胞公式计算方案在这里进行了改进，并根据无空位金云母的化学计量公式 XIIK2VIMg6IV[Si6Al2]O20（OH）4 对结果进行了测试。假设的片状硅酸盐组成，用与特定混合价元素取代相关的空位的固定含量计算，证实天然云母固体的可靠晶胞公式要求必须考虑每个化学计量空位。如果将“过量 O”（表示为 WO2−）的可靠估计分配给 EMP 分析，则可以定义氧云母组分在云母固溶体中的比例。该方法使用已发表的分析对分馏碱性和超基性火山火成岩中富含 Ti 和 Ba的生物矿物进行了测试（氧米菌范围 2.5-45 %;TiO2 高达 14 %;BaO 高达 23 %）、上地幔橄榄岩（等效值 7-18 %;6 %;0.7 %）和交代上地幔（2-37 %;9 %;23 %）。 云母中 Ti 和 Ba 的富集显然与中和电荷更高的 Ba2+ 和 Ti4+ 取代 K+ 和 Mg2+ 所需的额外氧电荷有关。