Al-Si Order and Chemical Composition Model across Scapolite Solid Solutions with Evidence from Rietveld Structure Refinements

IF 2.2 4区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Minerals Pub Date : 2024-08-11 DOI:10.3390/min14080812

Sytle M. Antao

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引用次数: 0

Abstract

Scapolite forms solid solutions between the end members marialite, Na4[Al3Si9O24]Cl = Me0, and meionite, Ca4[Al6Si6O24]CO3 = Me100. Al-Si order and chemical composition models are proposed for the scapolite solid solutions. These models predict the chemical composition, Al-Si order, and average distances between Me0–Me100. These models are based on the observed order of clusters and on two solid solutions that meet at Me75 coupled with predicted chemical compositions and distances. The [Na4·Cl]3+ and [NaCa3·CO3]5+ clusters are ordered between Me0–Me75, whereas the clusters [NaCa3·CO3]5+ and [Ca4·CO3]6+ are disordered from Me75–Me100. To confirm the structural model, the crystal structure of 27 scapolite samples between Me6–Me93 has been obtained using synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and Rietveld structure refinements. The structure was refined in space group P42/n for all the samples. The distances indicate that the T1 (=Si), T2 (=Al), and T3 (=Si) sites are completely ordered at Me37.5, where the 1:1 ratio of [Na4·Cl]3+:[NaCa3·CO3]5+ clusters are ordered and gives rise to antiphase domain boundaries (APBs) based on Cl-CO3 order instead of Al-Si order. The presence of APBs based on Cl-CO3 order and cluster order indicate that neither space group P42/n nor I4/m are correct for the structure of scapolite, but the lower symmetry space group P42/n is a good approximation for modeling the average structure of scapolite. The complete Al-Si order at Me37.5 changes in a regular and predictable manner toward the end members: Me0, Me75, and Me100. The observed unit cell and several structural parameters show a discontinuity at Me75, where the series is divided into two. There is no structural evidence to support any phase transition in the scapolite series. The T1 site contains only Si from Me0–Me37.5; from Me37.5–Me100, Al atoms enter the T1 site and the distance increases linearly to Me100.

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利用里特维尔德结构推演的证据建立整个闪锌矿固溶体的铝硅阶次和化学成分模型

皂石在端部成员 marialite（Na4[Al3Si9O24]Cl = Me0）和 meionite（Ca4[Al6Si6O24]CO3 = Me100）之间形成固溶体。提出了霞石固溶体的铝硅阶和化学成分模型。这些模型预测了化学成分、铝硅阶次和 Me0-Me100 之间的平均距离。这些模型是基于观察到的簇序和在 Me75 处相遇的两种固溶体，以及预测的化学成分和距离。[Na4-Cl]3+和[NaCa3-CO3]5+簇在Me0-Me75之间是有序的，而[NaCa3-CO3]5+和[Ca4-CO3]6+簇在Me75-Me100之间是无序的。为了证实该结构模型，利用同步辐射高分辨率粉末 X 射线衍射（HRPXRD）数据和里特维尔德结构细化，获得了 27 个介于 Me6-Me93 之间的霞石样品的晶体结构。所有样品的结构都是在 P42/n 空间群中细化的。距离显示，T1（=硅）、T2（=铝）和 T3（=硅）位点在 Me37.5 处完全有序，其中 1:1 比例的 [Na4-Cl]3+:[NaCa3-CO3]5+ 簇有序，并产生了基于 Cl-CO3 有序而非 Al-Si 有序的反相畴界（APB）。基于 Cl-CO3 有序和团簇有序的 APB 的存在表明，空间群 P42/n 或 I4/m 对于霞石的结构都不正确，但较低对称空间群 P42/n 是模拟霞石平均结构的良好近似值。Me37.5处的完整Al-Si阶以一种规律且可预测的方式向末端成员变化：Me0、Me75 和 Me100。观察到的单胞和几个结构参数在 Me75 处显示出不连续性，在该处系列被一分为二。没有任何结构证据支持皂石系列中的任何相变。从 Me0 到 Me37.5，T1 位点只含有硅；从 Me37.5 到 Me100，Al 原子进入 T1 位点，其距离线性增加到 Me100。

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来源期刊

Minerals MINERALOGY-MINING & MINERAL PROCESSING

CiteScore

4.10

自引率

20.00%

发文量

1351

审稿时长

19.04 days

期刊介绍： Minerals (ISSN 2075-163X) is an international open access journal that covers the broad field of mineralogy, economic mineral resources, mineral exploration, innovative mining techniques and advances in mineral processing. It publishes reviews, regular research papers and short notes. Our aim is to encourage scientists to publish their experimental and theoretical results in as much detail as possible. There is no restriction on the length of the papers. The full experimental details must be provided so that the results can be reproduced.