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Jinshajiangite: structure, twinning and pseudosymmetry.
Acta Crystallographica Section B ( IF 1.3 ) Pub Date : 2018-06-26 , DOI: 10.1107/s2052520618006753 Shiyun Jin 1 , Huifang Xu 1 , Seungyeol Lee 1 , Pingqiu Fu 2
Acta Crystallographica Section B ( IF 1.3 ) Pub Date : 2018-06-26 , DOI: 10.1107/s2052520618006753 Shiyun Jin 1 , Huifang Xu 1 , Seungyeol Lee 1 , Pingqiu Fu 2
Affiliation
The crystal structure of jinshajiangite based on a sample from its original discovery location is studied using single‐crystal X‐ray diffraction and transmission electron microscopy methods. Jinshajiangite is a titanium silicate mineral with an ideal chemical formula of BaNaFe4Ti2(Si2O7)2O2(OH)2F. The structure of jinshajiangite is of 
symmetry (triclinic system), with a = 8.7331 (2) Å, b = 8.7366 (2) Å, c = 11.0404 (3) Å, α = 81.477 (1)°, β = 110.184 (1)°, γ = 104.384 (1)° and V = 764.03 (3) Å3, instead of the previously proposed 
cell [a = 10.7059 (5) Å, b = 13.7992 (7) Å, c = 20.760 (1) Å, α = 90.008 (1)°, β = 94.972 (1)°, γ = 89.984 (1)°, V = 3055.4 (4) Å3]. The basic topology of the new structure is similar to the previously proposed structure, except there is only one type of titanium silicate and intermediate cation layer in the structure (instead of two types), which are all related by the translation along the c‐axis. Even though there is a significant amount of Mn in the chemical composition, no obvious ordering between Fe and Mn is observed in the structure. All the mineral species of the perraultite‐type structure (jinshajiangite, perraultite, surkhobite and bobshannonite) should have the same structure as jinshajiangite with ∼10 Å d001 spacing, and all the previously proposed monoclinic space groups were pseudosymmetry generated by nanoscale polysynthetic twinning on the (001) composition plane. The similar phenomenon observed in bafertisite is also discussed in the paper with an alternative polytype structure model proposed.
中文翻译：
金沙江岩：结构，孪生和假对称。
使用单晶X射线衍射和透射电子显微镜方法研究了金沙江岩的晶体结构，该数据来自原始发现地点的样品。Jinshajiangite是钛硅酸盐矿物与BaNaFe的理想的化学式4的Ti 2（SI 2 ö 7）2 Ô 2（OH）2 F. jinshajiangite的结构的对称性（三斜晶系），具有一个= 8.7331（2）埃，b = 8.7366（2）埃，c ^ = 11.0404（3）埃，α= 81.477（1）°，β= 110.184（1）°，γ= 104.384（1）°，V = 764.03（3）3，而不是先前建议的像元[ a = 10.7059（5）Å，b = 13.7992（7）Å，c = 20.760（1）Å，α= 90.008（1）°，β= 94.972（1）°，γ= 89.984（1）°，V = 3055.4（4）3 ]。新结构的基本拓扑与先前提出的结构类似，不同之处在于结构中只有一种类型的硅酸钛和中间阳离子层（而不是两种类型），它们都与沿c的平移有关-轴。即使在化学组成中存在大量的Mn，在结构中也未观察到Fe和Mn之间明显的有序性。所述perraultite型结构的所有矿物种（jinshajiangite，perraultite，surkhobite和bobshannonite）应具有相同的结构与jinshajiangite〜10埃d 001间距，以及由纳米级聚片双晶生成上伪对称所有先前提出的单斜晶系空间群（001）合成平面。本文还讨论了在钡铁矿中观察到的类似现象，并提出了另一种多型结构模型。
更新日期：2018-06-26
symmetry (triclinic system), with a = 8.7331 (2) Å, b = 8.7366 (2) Å, c = 11.0404 (3) Å, α = 81.477 (1)°, β = 110.184 (1)°, γ = 104.384 (1)° and V = 764.03 (3) Å3, instead of the previously proposed cell [a = 10.7059 (5) Å, b = 13.7992 (7) Å, c = 20.760 (1) Å, α = 90.008 (1)°, β = 94.972 (1)°, γ = 89.984 (1)°, V = 3055.4 (4) Å3]. The basic topology of the new structure is similar to the previously proposed structure, except there is only one type of titanium silicate and intermediate cation layer in the structure (instead of two types), which are all related by the translation along the c‐axis. Even though there is a significant amount of Mn in the chemical composition, no obvious ordering between Fe and Mn is observed in the structure. All the mineral species of the perraultite‐type structure (jinshajiangite, perraultite, surkhobite and bobshannonite) should have the same structure as jinshajiangite with ∼10 Å d001 spacing, and all the previously proposed monoclinic space groups were pseudosymmetry generated by nanoscale polysynthetic twinning on the (001) composition plane. The similar phenomenon observed in bafertisite is also discussed in the paper with an alternative polytype structure model proposed.
中文翻译：
金沙江岩：结构，孪生和假对称。
使用单晶X射线衍射和透射电子显微镜方法研究了金沙江岩的晶体结构，该数据来自原始发现地点的样品。Jinshajiangite是钛硅酸盐矿物与BaNaFe的理想的化学式4的Ti 2（SI 2 ö 7）2 Ô 2（OH）2 F. jinshajiangite的结构的
对称性（三斜晶系），具有一个= 8.7331（2）埃，b = 8.7366（2）埃，c ^ = 11.0404（3）埃，α= 81.477（1）°，β= 110.184（1）°，γ= 104.384（1）°，V = 764.03（3）3，而不是先前建议的像元[ a = 10.7059（5）Å，b = 13.7992（7）Å，c = 20.760（1）Å，α= 90.008（1）°，β= 94.972（1）°，γ= 89.984（1）°，V = 3055.4（4）3 ]。新结构的基本拓扑与先前提出的结构类似，不同之处在于结构中只有一种类型的硅酸钛和中间阳离子层（而不是两种类型），它们都与沿c的平移有关-轴。即使在化学组成中存在大量的Mn，在结构中也未观察到Fe和Mn之间明显的有序性。所述perraultite型结构的所有矿物种（jinshajiangite，perraultite，surkhobite和bobshannonite）应具有相同的结构与jinshajiangite〜10埃d 001间距，以及由纳米级聚片双晶生成上伪对称所有先前提出的单斜晶系空间群（001）合成平面。本文还讨论了在钡铁矿中观察到的类似现象，并提出了另一种多型结构模型。
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