多钙钾石膏(Grgeyite)晶体结构的精确修正

The Accurate Correction of the Crystal Structure of Grgeyite

本文利用直接法和富利叶合成测定了产于我国四川省三叠系蒸发岩里的多钙钾石膏的晶体结构,结构参数经最小二乘法修正后,R=0.084。结构分析表明,多钙钾石膏属单斜晶系,空间群C2/c,a=17.462(8),b=6.828(2),c=18.219(9),β=113.45(4)°,V=1992(1)~3,Z=4,Dm=2.91,Dx=2.90(3)。三个硫酸根四面体各自的平均S—O键长为1.467、1.464和1.478。有三套Ca原子,其中Ca_1在二次对称轴上。Ca原子的配位数为9,各自的平均Ca—O键长为2.516、2.515和2.459。K原子的配位数为8。首次测定了矿物中氢原子的位置,证实矿物含1个结晶水,而不是含1.5个结晶水。晶体化学式为K_2Ca_5(SO_4)_6·H_2O。

With the aid of automatic direct method and Fourier synthesis, the author has determined the crystal structure of grgeyite from Triassic evaporates in Sichuan province. The structure parameter corrected by least squares method is R=0.084. Structural analysis shows that grgeyite is of monoclinic system, with space group C2/c, a=17.462(8), b=6.828(2), c=18.219(9), β=113.45(4)°, V=1992(1)~3 Z=4,, Dm=2.91 and Dx=2.90(3). The mean lengths of S-O bonds of three sulfate tetrahedra are respectively 1.467, 1.464 and 1.478. There exist three sets of calcium atoms which have six-fold coordination with the mean lengths of Ca-O bonds being respectively 2.516, 2.515 and 2.459. Among these atoms, Ca_1 lies along the diad axis. The potassium atom has eight-fold coordination. The hydrogen atom in the mineral has been located for the first time, and it is proved that the mineral contains one molecule of crystalline water rather than 1.5 molecules. Its crystal chemical formula should therefore be K_2Ca_5(SO_4)_6H_2O.