Abstract Molecular formulae used to recalculate nepheline analyses generally have different numbers of oxygens (e.g. NaAlSiO4 (Ne), KAlSiO4, (Ks), CaAl2Si2O8 (An) and SiO2 (Q)). A 32 oxygen cell has 16 T cations and 8 cavity sites, but ideal nepheline stoichiometry is not necessarily followed. Ca end-member □CaCaAl2Si2O4 (CaNe) and excess silica end-member □SiSi2O4 (Q’) calculation requires inclusion of both vacancy species as cavity cation values. Q’ parameter calculations can involve different assumptions and four parameters are described: Qxs; QSi; Q(Si–Al); and Qcavity; these should have closely similar values for high-quality, stoichiometric analyses. Representative published compositions are recalculated to assess whether authors followed ideal nepheline stoichiometry. Phenocrysts from peralkaline rocks and nephelinites typically exhibit Al deficiencies reflected in negative Δ(Al – cavity cation) parameters (ΔAlcc), negative ‘normative’ corundum (Al2O3, Cn), and anomalously low or negative Qxs parameters; for such rock types Q(Si–Al) provides a better estimate of excess silica contents. A ΔT-site (cation charge) parameter (ΔTcharge), is closely coupled to ΔAlcc and end-member NaAlSiO4 has a ΔAlcc/ΔTcharge ratio of 1.4296; the derivation of this value is controlled by strict stuffed-tridymite, unit-cell constraints. Natural nephelines all contain excess silica with a mean ΔAlcc/ΔTcharge of ~1.134 reflecting their Si/Al ratio being > 1. Nepheline analyses with relatively low Al and Si and high Na (also Ca) contents are common; this might reflect the presence of small amounts (up to ~5%) of cancrinite as an alteration phase or perhaps even in solid solution. The compositions of alteration lamellae of Ca-rich cancrinite in altered nepheline phenocrysts in phonolites from the Marangudzi alkaline complex, Zimbabwe, are used to define diagnostic parameters for recognising such non-stoichiometry. These alteration lamellae formed hydrothermally from Ca-rich and K-poor fluids. An EXCEL file is provided to help researchers to standardise calculation of nepheline end-member molecular proportions.

中文翻译：

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霞石固溶体组成：重新审视、审查、澄清和合理化化学计量

摘要 用于重新计算霞石分析的分子式通常具有不同数量的氧（例如 NaAlSiO4 (Ne)、KAlSiO4、(Ks)、CaAl2Si2O8 (An) 和 SiO2 (Q)）。一个 32 氧电池有 16 个 T 阳离子和 8 个空腔位点，但不一定遵循理想的霞石化学计量。Ca 端元 □CaCaAl2Si2O4 (CaNe) 和多余的二氧化硅端元 □SiSi2O4 (Q') 计算需要包括两种空位物质作为空穴阳离子值。Q'参数计算可能涉及不同的假设，描述了四个参数：Qxs；QSi; Q(Si-Al); 和 Qcavity；对于高质量的化学计量分析，这些应该具有非常相似的值。重新计算代表性已发表的成分以评估作者是否遵循理想的霞石化学计量。来自过碱性岩石和霞石的斑晶通常表现出铝缺陷，反映在负 Δ(Al – 空腔阳离子) 参数 (ΔAlcc)、负“规范”刚玉（Al2O3、Cn）和异常低或负的 Qxs 参数中；对于此类岩石类型，Q(Si-Al) 提供了对过量二氧化硅含量的更好估计。ΔT 位点（阳离子电荷）参数 (ΔTcharge) 与 ΔAlcc 紧密耦合，端元 NaAlSiO4 的 ΔAlcc/ΔTcharge 比为 1.4296；该值的推导由严格的填充鳞屑、晶胞约束控制。天然霞石都含有过量的二氧化硅，平均 ΔAlcc/ΔTcharge 为 ~1.134，反映它们的 Si/Al 比 > 1。具有相对较低的 Al 和 Si 以及高 Na（以及 Ca）含量的霞石分析很常见；这可能反映了少量（高达约 5%）的钙化岩作为蚀变相或什至在固溶体中的存在。来自津巴布韦 Marangudzi 碱性复合体的响岩中改变的霞石斑晶中富含 Ca 的钙辉石的蚀变薄片的组成用于定义识别这种非化学计量的诊断参数。这些蚀变薄片是由富含钙和贫钾的流体热液形成的。提供了一个 EXCEL 文件来帮助研究人员对霞石端元分子比例的计算进行标准化。这些蚀变薄片是由富含钙和贫钾的流体热液形成的。提供了一个 EXCEL 文件来帮助研究人员对霞石端元分子比例的计算进行标准化。这些蚀变薄片是由富含钙和贫钾的流体热液形成的。提供了一个 EXCEL 文件来帮助研究人员对霞石端元分子比例的计算进行标准化。