XXVIII. The structure of sillimanite and mullite
XXVIII. The structure of sillimanite and mullite
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二十八．
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W. Taylor
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W. Taylor
介绍。三斜晶型Al%Si06的结构已经完全分析过了，但正交晶型和硅线石以及莫来石（^igiS^Ou）的单位胞和空间群已经确定。本文介绍了确定硅线石结构的分析方法，以及莫来石与硅线石的关系。W·k·k·f （greig和Bowen）检查了硅线石和莫来石的粉末、劳厄和单晶旋转照片，发现这两种晶体的照片几乎是相同的；然而，他们指出，某些微弱的反射，总是存在于硅线石的情况下，总是没有在莫来石照片。在这两种物质的粉末照片中存在着细微但明确的差异。马克和罗斯波特利用旋转晶体法，得到了与W·c·k·f、格里格和鲍恩相似的结果。这些实验结果可简述如下：- 1。硅线石ΑΙφίΟ$ （Al^Oz•SiO%）和莫来石AJ6Si2013（3 Al20s•2 Si02）这两种成分完全不同的化合物给出了几乎相同但不完全相同的x射线衍射数据。2. 从莫来石数据用通常的方法推导出的单元格只包含一个莫来石分子的四分之三——4磅铝，9磅铝，000个原子。在试图解释这些令人惊讶的结果时，人们认为最好是完全确定硅线石的结构
Introduction. The structure of the triclinic form of Al%Si06 has been completely analysed), but only the unit cells and space groups have been determined for the orthorhombic forms andalusile and sillimanite and for mullite (^igiS^Ou). The present paper describes the analysis leading to the determination of the structure of sillimanite, and the relationship existing between mullite and sillimanite. W y c k o f f , Gre ig and Bowen) have examined powder, Laue , and single-crystal rotation photographs for both sillimanite and mullite, and have found them to be almost identical for the two crystals; they state, however, that certain faint reflections, always present in the case of sillimanite, are always absent in mullite photographs. H y s l o p and Rooksby 3 ) have established the existence of slight but definite differences in powder photographs of the two substances, and Mark and Rosbaud 4 ) , using the rotating crystal method, have obtained results similar to those of W y c k o f f , Greig and Bowen. These experimental results may be stated briefly as follows: — 1. Two compounds of quite different composition, sillimanite ΑΙφίΟ$ (Al^Oz • SiO%) and mullite AJ6Si2013(3 Al20s • 2 Si02), give X-ray diffraction data which are almost but not quite identical. 2. The unit cell deduced in the usual way from the mullite data contains only threequarters of a molecule of mullite — 4 £ Al, 9-| 0, atoms. In making an attempt to explain these surprising results it has been thought best to determine the structure of sillimanite as completely as pos-