In this paper, grandite core with Grs64±1Adr36±1Sps2 composition was crystallographically studied. This core represents zone A of the macroscopically visible five A–E zones of the optically anisotropic Grs58–64Adr36–42Sps2 grandite. The applied procedure includes the detailed analysis of the powder diffraction patterns, and the Rietveld refinements of the crystal structures in a series of 18 space groups and two mixtures, which were followed by the comparative analysis of the R-values, site occupancy factors, and the bond lengths and angles. Synthesis of all of the presented results allows us to undoubtedly conclude that studied grandite is not cubic, neither as monophase nor as multiple phases in a mixture. Namely, it was established that structural dissymmetrization occurred and that it crystallized in the disordered rhombohedral $R\bar{3}c$ or orthorhombic Fddd space groups, whereby the first one is more probable. Beside the established lower symmetry of the studied grandite, which could be treated as the primary cause, the residual strain is also not excluded as the second possible cause for its slight optical anisotropy.

中文翻译：

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来自 Meka Presedla（Kopaonik Mt.，塞尔维亚）的光学各向异性 Grs64±1Adr36±1Sps2 巨石的结构不对称

在本文中，Gr64±1阿德尔36±1Sps2组成进行了晶体学研究。该核心代表光学各向异性 Grs 的宏观可见五个 A-E 区的 A 区58–64阿德尔36–42Sps2宏伟的。应用程序包括粉末衍射图案的详细分析，以及一系列 18 个空间群和两种混合物中晶体结构的 Rietveld 细化，然后对R-值、场地占有率以及键长和角度。综合所有呈现的结果，我们可以毫无疑问地得出结论，所研究的巨石不是立方的，既不是单相也不是混合物中的多相。即，确定发生结构不对称，并在无序的菱面体中结晶$R\bar{3}c$或斜方Fddd空间群，其中第一个更有可能。除了所研究的巨石确定的较低对称性（可被视为主要原因）外，残余应变也不排除作为其轻微光学各向异性的第二个可能原因。