斜方辉石空间群类型的重新确认

RECONFIRMATION OF THE SPACE GROUP FOR ORTHOPYROXENE

作者选择成分不同、产状各异的四个斜方辉石样品,分别沿其[100]方向进行了电子衍射分析。通过对实验结果的认真分析和充分论证,作者断定它们的空间群均为P2_1ca,而非Pbca。由于实验样品在成分和产状上均具有广泛的代表性,因此可以推断,在常温常压下,自然界的斜方辉石之空间群均为P2_1ca。

The [100] electron diffraction patterns have been taken for four orthopyroxenes collected from four types of rocks.(The composition of the end members ranges from En_(96.6) Fs_(3.4) Wo_0 to En_(47.6( Fs_(53.1) Wo_(1.1). ) The k odd diffractions themselves are completely present on these patterns. Based on the experimental observation and theoretical analysis, the authors believe that these k odd diffractions are caused neither by the overlap of certain diffractions from higher levels of orthopyroxene itself or clinopyroxene-C2/c exsolution Iamellae nor by the diffuse streaks along the a~* axis or the secondary diffraction effect. It is implied that there is no b-glide plane in the space group of orthopyroxene. As the four samples are of wide representation in composition and occu- rrence, the authors come to a conciusion that the space group oforthopyroxene should be P2_1ca, but not Pbca under normal pressure and temperature conditions.