Muscovite- and phengite-3T: crystal structure and conditions of formation
Muscovite- and phengite-3T: crystal structure and conditions of formation
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DOI：
10.1127/ejm/6/4/0489
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发表时间：
1994-08
影响因子：
2.1
通讯作者：
Alessandra Amisano-Canesi;G. Chiari;G. Ferraris;G. Ivaldi;S. Soboleva
中科院分区：
文献类型：
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作者：
Alessandra Amisano-Canesi;G. Chiari;G. Ferraris;G. Ivaldi;S. Soboleva
北哈萨克斯坦片岩中两种3 T多晶白云母的晶体结构（KZ; 6 < P < 9 kbar，T <600°C）和Dora-Maira Bagraf（意大利）的含辉石白片岩（DM; P = 30 kbar，T = 700°C）的晶体结构在空间群P3 1 12中被细化（单晶衍射仪; MoKα辐射; Rw = 0.037（KZ）和0.034（DM））。组成和电池参数如下：KZ：（K 0.93 Na 0.03）（Al 1.54 Fe 0.25 Mg 0.21 Ti 0.04）（Si 3.34 Al 0.66）O 10（OH）2，a = 5.212（1），c = 29.804（6）A; DM：（K0.92Na0.01）（Al1.41Mg0.60Ti0.02）（Si3.54Al0.46）O10（OH）2，a = 5.215（1），c= 29.755（5）尽管在两个样品中，两个独立的四面体位点没有显示出差异，但两个独立的八面体位点至少在几何上不同，特别是在DM的情况下。假设（i）高压有利于较少扭曲的结构和（ii）在3 T中存在两个独立的八面体填充位点允许更高的灵活性，3 T云母的结构特征与高压变质岩中多硅白云母-3T的更大丰度一致。这是根据多硅白云母-3T中的T和O片相对于白云母-3T更容易拟合来解释的，这是由于组成和单斜多硅白云母，其仅具有一个独立的填充八面体位点
The crystal structure of two 3T phengitic muscovites in schists from North Kazakhstan (KZ; 6 < P < 9 kbar, T ≃ 600°C) and in the pyrope-bearing whiteschists of the Dora-Maira massif (Italy) (DM; P ≃ 30 kbar, T ≃ 700°C) are refined in the space group P3 1 12 (single-crystal diffractometer; MoKα radiation; R w = 0.037 (KZ) and 0.034 (DM)). The compositions and cell parameters are as follows: KZ: (K 0.93 Na 0.03 )(Al 1.54 Fe 0.25 Mg 0.21 Ti 0.04 )(Si 3.34 Al 0.66 )O 10 (OH) 2 , a = 5.212(1), c = 29.804(6) A; DM: (K 0.92 Na 0.01 )(Al 1.41 Mg 0.60 Ti 0.02 )(Si 3.54 Al 0.46 )O 10 (OH) 2 , a = 5.215(1), c= 29.755(5) A. Whereas in both samples the two independent tetrahedral sites show no differences, the two independent octahedral sites differ at least geometrically, particularly in the case of DM. Assuming that (i) high pressure favours less distorted structures and (ii) the presence of two independent octahedral filled sites in 3T allows for higher flexibility, the structural features of 3T micas are consistent with a greater abundance of phengite-3T in high-pressure metamorphic rocks. This is explained in terms of easier fitting between T and O sheets in phengite-3T with respect to muscovite-3T, because of composition, and monoclinic phengite, which has only one independent filled octahedral site