Mn crystal chemistry in pumpellyite: A resonant scattering powder diffraction Rietveld study using synchrotron radiation
Mn crystal chemistry in pumpellyite: A resonant scattering powder diffraction Rietveld study using synchrotron radiation
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泵锰矿中的锰晶体化学：使用同步辐射的共振散射粉末衍射 Rietveld 研究
DOI：
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
M. Brr.
中科院分区：
文献类型：
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作者：
G. Anrror;A. PlvnsErr;M. Brr.
roOru,OH 和 Car,r(AlrnnMn.o,Mgo,Feo3o)Si,,84056 ,OH"。样品来自布拉科蛇绿岩（意大利东部利古里亚亚平宁山脉）的辉长角砾岩，其化学成分是与葡萄石-半辉石变质相中的锰矿化相关的典型富锰半辉石矿物。两个晶体学上独立的 X 和 Y 八面体位点上的 Mn 阳离子及其普遍的氧化态是通过使用同步加速器 X 射线对每个样品在不同波长处收集的多个粉末数据集进行 Rietveld 精修确定的。在靠近和远离 MnK 吸收边收集的粉末数据允许在 Rietveld 结构分析期间对每个数据集的 f' 反常散射参数以及其他变量进行精修，因此我们可以估计氧化。结果表明，泵锰矿中的 Mn 分布在两个八面体位点上，并且细化的异常散射系数清楚地表明两个 Mn 价态是分离的：Mn2+ 普遍存在于更对称的八面体 X 位点，Mn3+ 普遍存在于八面体 Y 位点。先前提出的泵贝利石是为了解释结构中铁阳离子的分布。
roOru,OH, and Car,r(AlrnnMn.o,Mgo,Feo3o)Si,,84056 ,OH". The samples are from gabbroic breccias of the Bracco ophiolites (Eastern Ligurian Apennines, Italy), and their chemistry is typical of Mn-rich pumpellyite minerals associated with Mn mineralization in prehnite-pumpellyite metamorphic facies. The distribution of the Mn cations over the two crystallographically independent X and Y octahedral sites, and their prevalent oxidation states, were determined by Rietveld refinement from multiple powder data sets collected at different wavelengths for each sample using synchrotron X-rays. The powder data, collected in proximity to and far from the MnK absorption edge, allowed refinement of the f' anomalous scattering parameter for each data set along with other variables during the Rietveld structure analysis, and we could thus estimate the oxidation state of Mn from the valence chemical shift of the absorption edge. The results indicate that Mn in pumpellyite is distributed over both octahedral sites, and the refined anomalous scattering coefficients clearly show that the two Mn valence states are segregated: Mn2+ is prevalent in the more symmetrical octahedral X site, and Mn3+ is prevalent in the octahedral Y site. The present results confirm the relationship between site partitioning and oxidation state oftransition elements in pumpellyite that was previously proposed to explain the distribution of Fe cations in the structure.