【摘要】 谢窦克等(1989)曾测定了大别山一个绿辉石的晶体结构,认为它具P2/c空间群;四面体链分别呈SA和OB扭转;M阳离子晶位全部为6次配位的八面体;Al在所有这四种晶位中均有相当多的占有率,为绿辉石的新型结构。本文对该资料再研究后确认其真实空间群为P2/n;结构中仅有一种O旋转的四面体链;M2和M2(1)晶位为8次配位;Al全部进入M1(1)晶位,Al-Mg呈完全有序分布,属典型的P2/n有序绿辉石。本文给出了重新计算的该绿辉石的结构数据,并对当前计算机使用日益广泛的情况下,在结构数据的处理中应更重视结晶学分析提出了看法。更多还原

【Abstract】 Xie Douke et al. (1989) determinated the crystal structure of omphacite from the Dabie Mountains. They affirmed that this crystal has space group P2/c, and in its structure, there are two kinds of tetrahedral chain with S-rotation and O-rotation respectively; the four symmetrically unequivalent M-sites are all 6-coordinated octahedra and Al exists in all of them with higher occupancies.A restudy on the data of this structure was carried out by the authors. It reveals that the true space group of the omphacite from the Dabie Mountains is P2/n rather than P2/c; and in its structure, there is only one kind of tetrahedral chain with O-rotation, the O3-O3-O3 chain angle is 170. 02% andM2 and M2(1) sites are of 8-coordination distinguished from 6-one of Ml and M1 (1) sites. In addition, the authors deem that, based on the M-O bond separation, all of Al should enter the smallest M1(1) site, while the site occupation between Al and Mg would be completely ordered. Thus, the structure mentioned above is a typical one of ordered omphacite with space group P2/n, rather than a new type P2/c structure for omphacite.The cause responsible for an incorrect space group is that the selection of the unit cell does not conform to the standard. The authors, therefore, recalculated the unit cell parameters and atom coordinates based on the data given by Xie Douke et al. , and furnish the correct ones here. Although some major errors have been found in the structural explanation given by Xie Douke et al. , the structural data are valuable.更多还原