The crystal structures and polytypism of bastnaesite-(Ce) (CeCO3F, B layer) and synchysite-(Ce) (CeCO3FWCaCO3, S layer) mineral series are very complicated in Sichuan Province, Southwest China. Four new polytypes: 6R, 2H2, 4H and 12H of the mixed-layer member CaCe3(CO3)4F3 (B2S) of this series were discovered by X-ray diffraction analyses and high resolution transmission electron microscopy, structural symmetry, cell and subcell parameters, possible space group, and structural stacking mode (dededgfg/T). They reveal that the mixed-layer member B2S is formed by the ordered stacking of two structural unit layers of bastnaesite-(Ce) (B layer) and one unit layer of synchysite-(Ce) (S layer) along the c direction. The forming of the new polytypes may depend on distributions and the periodical variation of orientation of the [CO3] groups between the unit layers of B2S. We have observed the {000l} microtwin of the 6R polytype and the syntactic intergrowths among the different polytypes formed by stacking faults in B2S.

According to the HRTEM study, the UHP jadeite-quartzite mineral (Rutile, TiO2) in Anhui Province, Dabie Mountains, China, has ultrastructures such as [011] two-dimensional commensurable modulated structures or superstructures, [011] twin domain structures, dislocations and crystal deformations. The SAED patterns and HRTEM images indicate the existence of the deformations and stacking faults on the interface of [011] twin crystal of rutile and its two-dimensional commensurate modulated structures with repetition period 0.753m (3d011) has tetragonal symmetry, cell parameters a=3a0=1:377nm (a0=0.459nm), c=c0=0:3nm. The modulated structures of rutile were probably caused by the isomorphic replacement of Ti4

The ultrastructures of parisite-(Ce) from a rare-earth mineral deposit of Sichuan Province, southwest China, have been observed and investigated by selected area electron diffraction (SAED) and high resolution electron microscopy (HREM). Six new polytypes 4H, 10H, 16H, 18R, 24R and 30R were determined in parisite-(Ce), as were their crystal structure types, subcell (a'c", a"c", a'c') and supercell(ac) parameters, reflection conditions, polytype features and probable space groups. The HREM studies revealed the complex polytypism in parisite-(Ce) whereby the six new polytypes, formed by longperiod ordered stacking, always coexist with the common polytype parisite-(Ce)-6R by syntaxy and thus constitute the complex microstructural 'syntactic polycrystals', the host of which is the polytype parisite-(Ce)-6R.

The microst ructural features of clacium-rare earth (Ca-RE) fluorocarbonate minerals f rom Southwest China were studied by using selected area elect ron diff raction (SAED) and high resolution transmission elect ron microscopy (HRTEM). Three new regularly mixed2layer st ruc-tures of B8S6 type with long period and different stacking sequence, i.e.B8S62 Ⅰ, B8S62 Ⅱ, andB8S6 2Ⅲ, were found in the derived polycrystal of parisite, in which their st ructural symmet ry, cell parameters, chemical formulas of crystal and stacking models of st ructural unit layer, etc. were determined. The result s of this study also show that these new regularly mixed2layer st ruc-t rues were formed by order stacking unit layer of bastnaesite (B) and synchisite (S) in varying pro-portion along c axis. The observation under HRTEM reveals that in the three new regularly mixed-layer st ructures there are different dist ribution modes of Ce2F ion layers, CO2-3 ion groups between the Ce2F ion layers, and CO2-3ion groups between Ce2F and Ca2+ion layers, and there are some heterogeneous textures, such as disorder interlayer and stacking fault. It further proves the complexity of the crystal st ructure of the Ca2RE fluorocarbonate minerals.

The process and path of retrometamorphism of coesite have great significance to our understanding of the P-T tracks of the exhumation of ultrahigh-pressure metamorphic rocks. Most of the coesites in the eclogite from Shima, Anhui Province, the Dabie Mountains, China, are found degraded to quartz partly or wholly, with ruptures occurring in the shells, outside which include the coesite and quartz. According to the microscopic observation, the sample of coesite inclusion is composed of garnet, quartz and coesite, based on which we have built a three-shelled composite sphere model to compute the transition of coesite. Based on the crystal growth formulas and pressure conditions of the ruptures in the garnet, we have calculated the radius of the quartz sphere, which depends on temperature, and eventually drawn the different retrometamorphic paths for different retrometamorphism rates.

Natural "monalbite" (MA) has been observed on a submicron-scale in jadeite along with high albite (HA) and low albite (LA) in jadeite quartzite in the Dabie ultrahigh-pressure (UHP) metamorphic terrane, China. Transmission electron microscope (TEM) observation of inclusions in jadeite crystals has revealed mineral phases with C2/m and C1-structures. The cell parameters of the C2/m crystal structure correspond to those of MA, whereas the cell parameters of C1-structure are identical to those of HA and LA. The existence of the C2/m structure shows that the jadeite underwent partial change to MA on a submicron-scale during retrograde metamorphism. Albite transformation twinning of HA suggests the transformation of MA into HA. MA occurrence provides powerful evidence of high-temperature metamorphism during exhumation, probably above 930℃. The preservation of MA may be due to the armouring by the jadeite and implies a very rapid cooling (quenching) during retrogression.

The domain structures in calcium cerium fluorocarbonate mineral series from a rare earth mineral deposit within an aegirine alkali granite massif in Mianning County, Sichuan Province, China, were studied by means of transmission electron microscopy. Many categories of domain structures in this mineral series were observed and in-vestigated, including the microtwin domains of parisite 6R2 and B2S 6R, the antiphase domains of B2S22H. The re-sults show that the antiphase domains which are faults along crystal plane (0001) are formed by the displacement of crystal lattice in c* direction and the displacement is 0.471nm. A new polytype (B4S2 3R) of regular mixed-layer structure with B4S2 type is found in the domain region of mixed layer structure.

The microst ructural characteristics of syntactic polycrystal in the calcium rare earth fluorocarbonate minerals f rom Southwest China have been studied by means of selected area elec t ron diff raction and high resolution elect ron microscopy (HREM). The complication of the hetero geneous fabric of the minerals have been revealed by HREM. The result s show that the crystal st ructure of the minerals was formed by a disorder stacking of the unit layers of bast naesite and synchisite in the calcium rare earth fluorocarbonate minerals along c direction. The stacking fault and other crystal defect s in the syntactic polycrystal have been discussed.

We present the results of high-resolution transmission electron microscope (HRTEM) studies on jadeite crystals of jadeite quartzite from the Dabie ultra-high-pressure (UHP) metamorphic terrane, China. Although jadeite is known to have only C2/c crystal structure, [100], [110], [112], [010] diffraction patterns and HRTEM images reveal C2/c and P21/n structures in 500 nm microdomains of single jadeite crystals, that we recognized in all the above four orientations. The cell parameters of C2/c crystal structure correspond to those of jadeite, whereas the cell parameters of P21/n structure are equivalent to those of omphacite. The presence of the P21/n structure shows that jadeite partially changed into omphacite on a nano-scale during retrograde metamorphism and that this reaction failed to reach equilibrium. It suggests uplift of the host rock during exhumation accompanied by complex non-equilibrium retrogressive process in the jadeite, with significant implications for the derivation of PT paths and tectonic interpretation of the Dabie UHP metamorphic terrane.

在大别山超高压变质带中发现的柯石英多数已经完全退变为聚晶石英，并伴随着包裹它的外层基质的破裂现象，通过对这一现象的分析可以揭示变质岩形成的一些历史信息。在透射电子显微镜（TEM）下可以观察到石榴石柯石英包裹体分为石榴石基质层，退变石英层和柯石英层，以此建立一个三层复合球模型。基质石榴石层的pT轨迹可以看成与已知的外界变质岩轨迹一样，而内部石英和柯石英层在基质发生破裂前可看成降压降温的生长退变过程，这一体积增大过程最终导致石榴石层的破裂。模型根据已知的大别山变质岩的温度变化速率，计算出石榴石柯石英包体的发生破裂的温度条件，并模拟柯石英不同退变程度所对应的不同路径，从而得出变质岩不同的抬升路径。