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Revealing the structures and relationships of Ca(II)–Fe(III)–AsO4 minerals: arseniosiderite and yukonite
Environmental Science: Nano ( IF 5.8 ) Pub Date : 2020-10-20 , DOI: 10.1039/d0en00503g
Graham King 1, 2, 3 , Mert Celikin 4, 5, 6, 7 , Mario Alberto Gomez 8, 9, 10, 11 , Levente Becze 3, 12, 13, 14 , Valeri Petkov 15, 16, 17, 18 , Giancarlo Della Ventura 19, 20, 21, 22
Affiliation  

The low crystallinity of arsenic (As) containing minerals such as arseniosiderite and yukonite has made a detailed understanding of their atomic structures elusive. X-ray pair distribution function (PDF) and transmission electron microscopy (TEM) were used to gain a detailed understanding of the short and medium-range structural features. High-resolution synchrotron powder diffraction data showed long-range order in arseniosiderite occurs along one direction. PDF data confirmed arseniosiderite has the same general structure as robertsite and mitridatite but with the layers occasionally shifted to disrupt long-range order. Use of small box and reverse Monte Carlo modeling of the PDF data gave the first complete set of atomic coordinates for arseniosiderite. TEM confirmed the degree of interlayer order is generally high. PDF and TEM data show that yukonite is a nano-sized analog of arseniosiderite which lacks any long-range order but is locally similar. The structural evolution of arseniosiderite from yukonite was observed for the first time in a natural specimen via TEM. PDF data on several yukonite samples reveal rather sudden drops in the degree of structural correlation as a function of distance. These drops occur from yukonite being composed of small layers made of integer numbers of large nonamers of edge-sharing FeO6 octahedra, as seen in arseniosiderite. However, these layers are 2 or 3 nonamers in width, with little structural correlation between layers. Thus our work provides a more complete nano/microscopic picture of the key structural features in these minerals found in mining ores and wastes around the world.

中文翻译:

揭示Ca(II)–Fe(III)–AsO4矿物的结构和关系:砷铁矿和育空石

砷(As)的矿物如砷铁矿和育空石等矿物的结晶度较低,因此对其原子结构的详细了解难以捉摸。X射线对分布函数(PDF)和透射电子显微镜(TEM)用于获得对短程和中程结构特征的详细了解。高分辨率同步加速器粉末衍射数据显示,亚砷酸亚铁中的长程有序沿一个方向发生。PDF数据确认,亚砷铁矿具有与菱铁矿和三菱铁矿相同的一般结构,但层间不时地移动以破坏远距离有序。PDF数据的小方块和反向蒙特卡洛建模的使用为砷铁矿提供了第一套完整的原子坐标。TEM证实层间有序度一般较高。PDF和TEM数据表明,育空石是一种亚砷酸亚铁的纳米级类似物,它缺乏任何长程有序性,但局部相似。首次在天然标本中观察到了由Yukonite产生的砷铁矿的结构演变通过TEM。几个育空石样品上的PDF数据显示,结构相关程度随距离而突然下降。这些液滴是由育空石形成的,其由小数目的层组成,该小层由整数个边缘共享的FeO 6八面体的大九聚体构成,如亚砷酰胺中所见。但是,这些层的宽度为2或3个九聚体,层之间的结构相关性很小。因此,我们的工作为全球采矿和废物中发现的这些矿物的关键结构特征提供了更完整的纳米/显微图片。
更新日期:2020-11-03
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