EXCALIBR to EXCELIBR and the optical orientation of minerals: Correcting the optical orientation of clinoamphiboles
EXCALIBR to EXCELIBR and the optical orientation of minerals: Correcting the optical orientation of clinoamphiboles
复制标题
EXCALIBR 到 EXCELIBR 和矿物的光学取向：校正斜角闪石的光学取向
DOI：
10.2138/am-2020-7336ccbyncnd
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发表时间：
2020
影响因子：
3.1
通讯作者：
M. Gunter
中科院分区：
文献类型：
--
作者：
C. Steven;M. Gunter
摘要自从角闪石在C2/m中标准化以来，C2/m角闪石的晶体学取向一直被错误地描述。引用了早期关于角闪石的光学工作的文本参考了在I2/m单元中绘制的结构，其光学方向是正确的。当C2/m成为标准空间群时，光学取向（hkl）和晶形图中描绘的晶轴从未被修改。使用Gunter和Twamley（2001）概述的方法，结合X射线和光学方法对角闪石单晶进行研究，揭示了轴之间的差异。在典型的C2/m角闪石的正确取向中，物理光学取向应该永远不会从福特和达纳（1932）所示的切马克设置中概述的位置改变，但是，晶轴和（hkl）应该改变以适应I2/m晶胞和C2/m晶胞之间的差异。这种错误可能会使斜闪石的晶体学设置和光学取向之间的误解永久化，这是依赖于取向的分析方法的一个重要关系。在这项研究中所描述的是C2/m角闪石的晶形图的晶轴的校正，沿着与方法的大纲和电子表格EXCELIBR的更新。在这项研究中应用的方法利用晶体学和光学矢量之间的关系，包括Gunter和Twamley（2001）提出的方法的附录，适用于主轴台上的任意参考位置。
Abstract The crystallographic orientation of C2/m amphiboles has been depicted incorrectly since the standard‑ ization of amphiboles in C2/m. Texts citing the early optical work on amphiboles reference structures drawn in the I2/m cell, for which the optical orientation is correct. When C2/m became the standard space group, the optical orientation (hkl), and crystallographic axes depicted in crystal form drawings were never revised. Using the methods outlined by Gunter and Twamley (2001) combined with X‑ray and optical methods on single crystals of amphiboles reveals the discrepancy between axes. In the cor‑ rect orientation of a typical C2/m amphibole, the physical optical orientation should have never changed from its position outlined in the Tschermak setting as shown in Ford and Dana (1932), however, the crystallographic axes and (hkl) should have changed to accommodate the difference between the I2/m cell and the C2/m cell. This error may perpetuate a misunderstanding between the crystallographic setting and optical orientation of clinoamphiboles, which is an important relationship for orientation-dependent analytical methods. Described in this study is the correction of crystallographic axes for crystal form drawings for C2/m amphiboles, along with an outline of methodology and updates to the spreadsheet EXCELIBR. The methods applied in this study utilize relationships between crystallographic and optical vectors and include an addendum to those presented by Gunter and Twamley (2001), which is applicable to arbitrary reference positions on spindle stages.