钙稀土氟碳酸盐矿物中新多型体的HREM研究

利用高分辨电子显微术（ＨＲＥＭ）研究了钙稀土氟碳酸盐矿物系列中氟碳铈矿（Ｂ）／直氟碳钙铈矿（Ｓ）的混层结构。发现并确定了Ｂ＿５Ｓ＿２（ＩＨ，３Ｒ）、Ｂ＿５Ｓ＿４（３Ｒ，６Ｒ）和Ｂ＿（１８）Ｓ＿（１０）（ＩＨ）规则混层矿物中５种新多型的晶体结构类型、晶胞参数以及理论晶体化学式等。ＨＲＥＭ研究揭示出，在Ｂ＿ｍＳ＿ｎ（ｍ＞ｎ）型规则混层矿物新多型体的结晶过程中，成矿地质环境是复杂的。阐明了这些多型体是由该系列矿物中的氟碳铈矿（Ｂ）和直氟碳钙铈矿（Ｓ）结构单元层以不同比例沿ｃ轴方向的有序堆垛构成。

A Study of New Polytypes in the Calcium Rare-Earth Fluoro-carbonate Minerals under High Resolution Transmission Electron Microscope

Mixeod -later strucure in the calcium rare-earth fluorocarbonate mineral series has been studied with high resolution electron microscopy(HREM). Five new polytypes,i.e. ,B_5S_2-1H and 3R, B_5S_4-3R and 6R,B_(18)S_(10)-1H,were discovered in the crystal structure of parisite(BS).For the five new poly-types,the electron diffraction regularity,the crystal structural type and the space symmetry were determined.The complicacy of metallogenic geological environment during the crystallization of new polytypes in the regularr mixed-layer mineral of the type B_mS_n(m>n)has been revealed by means of the solected area electron diffraction ( SAED)and HREM.The results show that these regular mixed-layer minerals and new polytypes are usually found coe-xisting in one natural grain of parisite as the syntactic intergrowth.However,the regular mixed-layer minerals and new polytypes with long-peried ordered stacking sequence are much fewer than those short-period disorder stack-ing sequence.These new polytypes can be considered as containing layer of bastnaesite(B)and synchisite(S)in the series by ordercd stacking in vary-ing proportions along c axis.