Average Structures of Alkali and Plagioclase Feldspars: Systematics and Applications
Average Structures of Alkali and Plagioclase Feldspars: Systematics and Applications
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碱长石和斜长石的平均结构：系统学和应用
DOI：
10.1007/978-94-015-6929-3_1
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发表时间：
1984
期刊：
影响因子：
--
通讯作者：
P. Ribbe
中科院分区：
文献类型：
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作者：
P. Ribbe
本文综述了碱金属和斜长石的结构系统学及其各种空间群对称性与A-阳离子化学和Al、Si含量、Al、Si有序-无序和温度的关系。伪对称性和网站命名所产生的位移和扩散相变的背景下进行描述。建立了真实结构（可能包括双晶胞、反相畴、精细的超结构、亚微观和亚调幅出溶织构以及产生的应变相）与平均结构之间的关系。平均结构的概念涉及到“投影”的立体细节的真实的结构上的Cnalbite或C2/msanidine细胞只包含一个A-阳离子网站和4或2个对称非等效四面体网站，分别。因此，一种非常复杂的“e”型斜长石或斜长石或过渡型钙长石（c ~14.2）可以简化为一个简化的，“平均”结构模型，它主要用于建立对容易测量的度量参数和光学性质的变化的理解。为了将从晶体结构精修获得的平均四面体键长转换为特定四面体（T）位点的Al/（Al+Si）含量，碱和斜长石结构的大多数现代改进重新评估和系统地检查与它们的晶格参数的关系，这些晶格参数本身在很大程度上是平均结构的量度。本文提出了一些改进的成分和结构状态测定方法，包括碱性长石的b-c、α ~*-γ ~*、[110]、[110]图和斜长石的[110]、[110]、Δ131和γ图。描述了使用光轴角2 V作为富钾碱性长石结构状态的精确测量（来自Su等人，1983 a，B）。
The structural systematics of alkali and plagioclase feldspars and the details of their various space group symmetries are reviewed in relation toA-cation chemistry and Al,Si content, to A1,Si order-disorder, and to temperature. Pseudosymmetry and the site nomenclature arising from it are described in the context of displacive and diffusive phase transformations. The relation betweenrealstructures (which may involve doubled unit cells, antiphase domains, and elaborate superstructures, as well as spinodal and submicroscopic exsolution textures and resuloing strained phases) andaveragestructures is established. The average structure concept involves “projecting” the steric details of the real structure onto the Cī albite orC2/msanidine cell which contain only oneA-cation site and 4 or 2 symmetrically nonequivalent tetrahedral sites,respectively. Thus an intensely complex ‘e’-plagioclase or aPī or transitional anorthite (withc ~14.2 Å) may be reduced to a simplified, “average” structural model which has its primary usefulness in establishing an understanding of the variation of easily measured metric parameters and optical properties.The new method of Kroll and Ribbe (1983) for converting the mean tetrahedral bond lengths obtained from crystal structure refinements to Al/(Al+Si) contents of particular tetrahedral (T) sites is reiterated, and most modern refinements of alkali and plagioclase structures are re-evaluated and systematically examined in relation to their lattice parameters, which are themselves—for the most part—measures of theaveragestructure. Revised compositional and structural state determinative methods are presented, including theb-c, α*-γ*, and [110],[1ī0] plots for alkali feldspars and [110],[1ī0], Δ131 and γ plots for plagioclases. The use of the optic axial angle 2V as a precise measure of structural state in K-rich alkali feldspars is described (from Su et al., 1983a,b).