伟晶岩型铝硅酸盐矿物的晶体化学特征计算与分析

Theoretical Calculation and Analysis of Crystallochemical Characteristic of Pegmatite Aluminosolicate Minerals

探讨了伟晶岩型铝硅酸盐矿物(锂辉石、长石和云母)的晶体结构,三者晶体结构最大不同之处在于Al—O配位方式不同。其中,锂辉石晶体结构中Al在硅氧四面体骨干之外,以六配位的形式组成[AlO_6]八面体;钠长石晶体结构中Al取代了Si呈[AlO_4]四面体;而白云母晶体结构中[AlO_4]四面体和[AlO_6]八面体同时存在。同时,以键价的观点对这三种矿物晶体结构中化学键的特征进行理论计算。结果发现,M^(n+)静电价强度、M^(n+)—O^(2-)键平均键长、库仑力、平均键价之间具有极好的一致性。在伟晶岩型铝硅酸盐矿物结构中,[SiO_4]四面体Si—O键是最强的,当Al取代Si时,[AlO_4]四面体中Al—O键的键强次之,[AlO_6]八面体Al—O键的键强较弱,其它金属M—O键的键强最弱。

The crystal structures of pegmatite aluminosilicate minerals （ spodumene, feldspar and mica） were investigated. The largest difference among them is the different coordination of AI--O. For spodumene, Al is outside of silicon oxygen tetrahedron backbone outside, and in the form of six coordination of octahedron [ AlO6 ]. For albite, Si is replaced by Al and in the form of tetrahedron [ AlO4 ]. And for mica, tetrahedron [ AlO4 ] and octahedron [ AlO6] exist at the same time. Based on rule of bonding-valence, the characteristics of chemical bonds in the three minerals crystal structure were theoretical calculated. The results show that the static electricity intensity of Mn~ , average bond length of Mn＋-O2- , coulomb force, and the average bond valence have the very good consistency. In the pegmatite aluminosilicate minerals structures, the Si--O bond strength in tetrahedron [ SiO4 ] is the strongest, AI--O bond strength in tetrahedron [ AlO4] where A1 replace Si is stronger, AI--O bond strength in the octahedral [ AlO6 ] is weak, other M--O bond strength is the weakest.