The method of ionic network analysis [Thomas (2017). Acta Cryst. B73, 74–86] is extended to tectosilicates through the example of coesite, the high‐pressure polymorph of SiO₂. The structural refinements of Černok et al. [Z. Kristallogr. (2014), 229, 761–773] are taken as the starting point for applying the method. Its purpose is to predict the unit‐cell parameters and atomic coordinates at (p–T–X) values in‐between those of diffraction experiments. The essential development step for tectosilicates is to define a pseudocubic parameterization of the O₄ cages of the SiO₄ tetrahedra. The six parameters a_PC, b_PC, c_PC, α_PC, β_PC and γ_PC allow a full quantification of the tetrahedral structure, i.e. distortion and enclosed volume. Structural predictions for coesite require that two separate quasi‐planar networks are defined, one for the silicon ions and the other for the O₄ cage midpoints. A set of parametric curves is used to describe the evolution with pressure of these networks and the pseudocubic parameters. These are derived by fitting to the crystallographic data. Application of the method to monoclinic feldspars and to quartz and cristobalite is discussed. Further, a novel two‐parameter quantification of the degree of tetrahedral distortion is described. At pressures in excess of ca 20.45 GPa it is not possible to find a self‐consistent solution to the parametric curves for coesite, pointing to the likelihood of a phase transition.

中文翻译：

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硅酸盐硅酸盐的离子网络分析：变压石英岩的例子。

离子网络分析方法[Thomas（2017）。Acta Cryst。乙73，74-86]通过柯石英的SiO的高压多晶型物的示例扩展到网状硅酸盐₂。Černok等人的结构改进。[ Z. Kristallogr。（2014），229，761-773]被作为用于施加方法的起点。其目的是在衍射实验之间的（p – T – X）值处预测晶胞参数和原子坐标。硅酸盐硅酸盐的基本开发步骤是定义SiO ₄的O ₄笼的拟立方参数化四面体。六个参数一个_PC，b _PC，Ç _PC，α _PC，β _PC和γ _PC允许四面体结构的一个完整的量化，即扭曲和封闭容积。柯氏体的结构预测要求定义两个单独的准平面网络，一个用于硅离子，另一个用于O ₄笼子中点。一组参数曲线用于描述这些网络的压力和伪三次参数的演化。这些是通过拟合晶体学数据得出的。讨论了该方法在单斜长石以及石英和方石英上的应用。此外，描述了新颖的四面体畸变程度的两参数量化。在超过约20.45 GPa的压力下，无法找到余弦参数曲线的自洽解，从而指出了相变的可能性。