【摘要】 自然界中绿柱石晶体多为柱状,具板状晶形的绿柱石非常少见。本文对产于四川雪宝顶云英岩晶洞中的无色透明板状绿柱石进行了精确的结构分析,并与产于阿尔泰三号伟晶岩脉中的柱状绿柱石进行了比较。与阿尔泰柱状绿柱石相比,雪宝顶板状绿柱石富Li、Na,c/a值较高,为1.001,属钠-锂绿柱石或“四面体”绿柱石。本文还对这种特殊形貌绿柱石的形成机制进行了初步讨论,成矿流体中Li的浓度以及Si的化学形态可能是影响绿柱石形貌的重要因素。更多还原

【Abstract】 Beryl crystals occurring in nature are mostly prismatic, tabular ones are rarely observed. This paper presents a study of the structure of a tabular crystal of beryl from the Xuebaoding greisen, and a comparisons with a prismatic crystal sample of beryl from the Altay pegmatite. The beryl of Xuebaoding is rich in Li and Na, containing 0. 71 % of Li2O and 1. 59 % of Na2O. And it has a relatively high c/a ratio of 1. 001. These facts show that the beryl of Xuebaoding belongs to the Na-Li beryl or "tetrahedral" beryl. The data of diffraction intensity of the crystal structure were obtained with the Siemens P4 four-circle diffractometer. The structures were solved by direct methods and were refined to R indices of 2 % - 3 %. The results show that substitution of Be by Li caused the Be-O bond distance to expand. The formation mechanism of the tabular morphology of beryl is also discussed in the paper. The content of and/or chemical form of Si in the ore-forming fluid may be one of the important factors affecting the morphology of beryl crystals.更多还原