Interlayer structure in aspidolite, the Na analogue of phlogopite
Interlayer structure in aspidolite, the Na analogue of phlogopite
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DOI：
10.1127/0935-1221/2004/0016-0891
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发表时间：
2004-11
影响因子：
2.1
通讯作者：
T. Kogure;Y. Banno;R. Miyawaki
中科院分区：
文献类型：
--
作者：
T. Kogure;Y. Banno;R. Miyawaki
人们发现，金云母的钠类似物——云云母，具有与云母不同寻常的层间结构。研究的硅云母与热变质岩中的金云母交错。电子微探针化学分析显示，除了钠和钾的层间阳离子外，云母和金云母的成分相似。高分辨率透射电子显微镜 (HRTEM) 显示，对于所有 2:1 层，层内位移（2:1 层中两个四面体片之间的位移）的方向是均匀的，a /3 朝向 [100]，并且钠和钾被分解到不同的层间区域，从而在单层水平上形成两个云母的层间化。 HRTEM 和电子衍射分析表明存在较大的层偏移，即跨含钠夹层区域的两个四面体片之间的横向偏移。层偏移量约为0.9A（约16），方向为[100]、[110]和[110]之一。这些方向有时是混乱的。通过层内位移和层偏移的结合，有序的云杉具有不同的一层结构，具有单斜晶格（[100]层偏移）和三斜晶格（[110]或[110]层偏移）细胞。对于单斜晶格 ( C 2/ m )，建议的晶格尺寸为 a = 5.30、b = 9.18、c = 10.12 A、β = 105.3°；对于三斜晶格 ( C 1)，建议晶格尺寸为 a = 5.30、b = 9.18、c = 9.88 A、α = 94.4、β = 97.8、γ = 90°细胞。这两种结构均在粉末 X 射线衍射图中得到鉴定，并且可能三斜结构更为常见。这是第一份关于层内位移和层偏移相结合在云母中产生结构变化的报告。
It has been found that aspidolite, the Na analogue of phlogopite, has an unusual interlayer structure for micas. The aspidolite investigated is interleaved with phlogopite in a thermally metamorphosed rock. Electron microprobe chemical analyses showed similar compositions for aspidolite and phlogopite except interlayer cations of sodium and potassium. High-resolution transmission electron microscopy (HRTEM) revealed that the direction of the intralayer shift (shift between the two tetrahedral sheets in a 2:1 layer) is uniform, a /3 toward [100], for all 2:1 layers, and that sodium and potassium are resolved to different interlayer regions to form interstratification of the two micas at monolayer level. HRTEM and electron diffraction analyses indicate a large layer offset, i.e. , lateral shift between the two tetrahedral sheets across the sodium-bearing interlayer region. The amount of the layer offset is about 0.9 A ( ca. a 16) and the direction is one of [100], [110] and [110]. These directions are occasionally disordered. By combination of the intralayer shift and layer offset, the ordered aspidolite has different one-layer structures with monoclinic ([100] layer offset) and triclinic ([110] or [110] layer offset) cells. The proposed cell dimensions are a = 5.30, b = 9.18, c = 10.12 A, β = 105.3° for the monoclinic ( C 2/ m ) cell and a = 5.30, b = 9.18, c = 9.88 A, α = 94.4, β = 97.8, γ = 90° for the triclinic ( C 1) cell. Both structures were identified in powder X-ray diffraction patterns and probably the triclinic structure is more common. This is the first report that structural variations are generated in micas by the combination of the intralayer shift and layer offset.