对于氟碳钡铈矿（Cordylite—Ce）成分与结构的质疑

本文讨论了氟碳钡铈矿的成分和结构问题。发现氟碳钡铈矿的成分、密度、折射率三者间的一致性参数很差,晶体结构与光性和空间群相矛盾,单个大阳离子的平均占有体积远大于同类矿物的平均占有体积,它的晶体结构与同类矿物不可类比。由于受当时条件的限制,在以往有关氟碳钡铈矿的成分和结构的资料中存在着一些明显的错误,有必要对其进行重新定义。其结构化学式应改为:(Na_(1-x),Ca_(0·5x))BaCe_2(CO_3)_4F。

New Data on Cordylite-(Ce)

A careful study of cordylite-(Ce), a barium rare earth fluor-carbonatemineral, has yielded the following results: (1) The compatibility values (1-K_p/K_c) of cordylite-(Ce) are verylow (-0.1896 and -0.2139 respectively for data given by Chen (1975) andideal chemical composition). (2) The structure of cordylites (Ce) assumedby Oftedal (1931) is in contradiction with its optical properties and spacegroup. (3) The mean occupied volume of a single large cation (unit cellvolume/number of large cations per cell) of cordylite-(Ce) is unusual (86.2A~3), i. e. it is much larger than the volume in similar minerals such as ce-baite- (Ce)and huangheite-(Ce)(about 72 A~3).(4) Cordylite-(Ce) has no coor-dination polyhedra similar to those in huangheite-(Ce) etc. (5) The struc-ture of cordylite-(Ce) can not be compared with that of similar minerals.The previously-given chemical composition and structure of cordylite-(Ce)is therefore incorrect, and the formula of cordylite-(Ce) should be expressedas (Na_1-x, Ca_0.5x) BaCe_2, (CO_3)_4F.