MICROSCOPIC GEOLOGICAL ABNORMALITY AND ITS SIGNIFICANCE OF RARE EARTH MINERALS IN ALKALI GRANITE
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摘要: 四川冕西霓石碱性花岗岩中的稀土矿物主要为钙稀土氟碳酸盐矿物系列, 通过选区电子衍射(SAED)和高分辨透射电子显微术(HRTEM)研究发现该系列矿物晶体结构中广泛发育复杂多样的微观地质异常现象, 其主要类型有: (1)由该系列两个端员矿物氟碳铈矿结构层(B)与直氟碳钙铈矿结构层(S)以不同比例沿c轴方向有序堆垛形成的BmSn型规则混层结构; (2)无序堆垛形成的有序-无序结构晶畴; (3)由堆垛层错形成的无序混层结构、氟碳钙铈矿中不同多型体间的共格连生结构和相转变等; (4)氟碳铈矿结构中的平行于[0001]方向的平移畴及一维无公度调制结构, 该类调制结构可能是由于矿物中原子占位有序度的变化而形成的无序结构状态.
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关键词:
- 稀土矿物 /
- 混层 /
- 多型 /
- 调制结构 /
- 高分辨透射电子显微术
Abstract: The rare-earth minerals within aegirine alkali granite from Mianning, Sichuan Province are mainly the calcium-rare-earth fluorocarbonate series. In this paper, the complicated, various geological abnormality is discovered by means of the selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) : (1) the regular mixed-layer structure BmSn formed by the ordered stacking of the unit layers in bastnaesite (B) and synchysite (S) of this series in different scales along c direction; (2) the ordered-disordered domain structures formed by the disordered stacking; (3) the disordered mixed-layer structure formed by the stacking faults, the syntactic intergrowth and phase transition among different polytypes in parisite; (4) the translation domains parallel to the direction in bastnaesite and the one-dimensional immensurate modulated structures which are probably disordered structures formed by the change of the ordered degree of atom occupations.-
Key words:
- rare-earth mineral /
- mixed-layer /
- polytype /
- modulated structure /
- HRTEM
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图 1 钙稀土氟碳酸盐矿物中的B2S (a)、新规则混层矿物B5S4 (b)、BmSn结构间的有序-无序堆垛(c) 和氟碳钙铈矿中的无序堆垛结构(d)
Fig. 1. B2S of calcium-rare-earth fluorocarbonate minerals (a), new, regular, mixed-layer mineral B5S4 (b), the order-disorder stacking among BmSn structures (c) and the disorder stacking structure in parisite (d)
图 2 氟碳钙铈矿6R1与6R2多型体间的共格连生结构(a)、氟碳铈矿晶体中的调制结构(b) 及平移畴结构(c)、B2S规则混层结构中的层错(或相转变) (d)
Fig. 2. Syntaxy structure between polytypes parisite-6R1 and parisite-6R2 (a), modulated structure (b) and the translation domain structure (c) in bastnaesite crystal, and faults (or phase transformation) in B2S regular mixed-layer structure (d)
表 1 钙稀土氟碳酸盐矿物晶体结构特征
Table 1. Crystal structures of Ca-REE fluorocarbonate minerals
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