On the crystal-chemistry of inderite, Mg[B3O3(OH)5](H2O)4·H2O

IF 1.2 4区地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY

Physics and Chemistry of Minerals Pub Date : 2024-05-23 DOI:10.1007/s00269-024-01281-w

G. Diego Gatta, Silvia C. Capelli, Davide Comboni, Enrico Cannaò

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Abstract

The crystal chemistry of inderite, a hydrous borate with known ideal formula MgB₃O₃(OH)₅·5H₂O from the Kramer deposit, was re-investigated by electron probe micro-analysis in wavelength dispersive mode, laser ablation-(multi collector-)inductively coupled plasma-mass spectrometry and single-crystal neutron diffraction. The chemical data prove that the real composition of the investigated inderite is substantially identical to the ideal one, with insignificant content of potential isomorphic substituents, so that, excluding B, inderite does not contain any other industrially-relevant element (e.g., Li concentration is lower than 2.5 wt ppm, Be or REE lower than 0.1 wt ppm). The average δ¹¹B_NIST951 value of ca. − 7 ‰ lies within the range of values in which the source of boron is ascribable to terrestrial reservoirs (e.g., hydrothermal brines), rather than to marine ones. Neutron structure refinements, at both 280 and 10 K, confirm that the building units of the structure of inderite consist of: two BO₂(OH)₂ tetrahedra (B-ion in sp³ electronic configuration) and one BO₂(OH) triangle (B-ion in sp² electronic configuration), linked by corner-sharing to form a (soroborate) B₃O₃(OH)₅ ring, and a Mg-octahedron Mg(OH)₂(OH₂)₄. The B₃O₃(OH)₅ ring and the Mg-octahedron are connected, by corner-sharing, to form an isolated Mg(H₂O)₄B₃O₃(OH)₅ (molecular) cluster. The tri-dimensional edifice of inderite is therefore built by heteropolyhedral Mg(H₂O)₄B₃O₃(OH)₅ clusters mutually connected by H-bonds, mediated by the zeolitic (“interstitial”) H₂O molecules lying between the clusters, so that the correct form of the chemical formula of inderite is Mg[B₃O₃(OH)₅](H₂O)₄·H₂O, rather than MgB₃O₃(OH)₅·5H₂O. All the thirteen independent oxygen sites of the structure are involved in H-bonding, as donors or as acceptors. This confirms the pervasive nature and the important role played by the H-bonding network on the structural stability of inderite. The differences between the crystal structure of the two dimorphs inderite and kurnakovite are discussed.

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关于橄榄石（Mg[B_3O_3(OH)_5](H_2O)_4-H_2O）的晶体化学性质

通过波长色散模式下的电子探针显微分析、激光烧蚀-（多收集器-）电感耦合等离子体-质谱法和单晶中子衍射法，对克拉玛依矿床中已知理想分子式为 MgB3O3（OH）5-5H2O 的水合硼酸盐英得莱石的晶体化学进行了重新研究。化学数据证明，所研究的橄榄石的实际成分与理想成分基本相同，潜在的同构取代基含量极少，因此，除 B 外，橄榄石不含任何其他工业相关元素（例如，锂浓度低于 2.5 wt ppm，Be 或 REE 低于 0.1 wt ppm）。δ11BNIST951 的平均值约为 7 ‰。- 平均δ11BNIST951值约为7‰，属于硼源可归因于陆地储层（如热液卤水）而非海洋储层的数值范围。在 280 开氏度和 10 开氏度下进行的中子结构细化证实，橄榄石结构的组成单元包括：两个 BO2(OH)2 四面体（sp3 电子构型的硼离子）和一个 BO2(OH) 三角形（sp2 电子构型的硼离子），它们通过角共享连接成一个（山梨硼酸盐）B3O3(OH)5 环，以及一个镁八面体 Mg(OH)2(OH2)4。B3O3(OH)5环和八面体镁通过分角连接，形成一个孤立的Mg(H2O)4B3O3(OH)5（分子）簇。因此，橄榄石的三维结构是由异多面体 Mg(H2O)4B3O3(OH)5簇通过 H 键相互连接而成的，并由位于簇之间的沸石（"间隙"）H2O 分子介导，因此橄榄石的正确化学式是 Mg[B3O3(OH)5](H2O)4-H2O，而不是 MgB3O3(OH)5-5H2O。该结构中所有 13 个独立的氧位点都参与了氢键作用，无论是作为供体还是作为受体。这证实了 H 键网络对橄榄石结构稳定性的普遍性和重要作用。本文还讨论了英达石和库尔纳克维石这两种非晶态晶体结构之间的差异。

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来源期刊

Physics and Chemistry of Minerals 地学-材料科学：综合

CiteScore

2.90

自引率

14.30%

发文量

审稿时长

3 months

期刊介绍： Physics and Chemistry of Minerals is an international journal devoted to publishing articles and short communications of physical or chemical studies on minerals or solids related to minerals. The aim of the journal is to support competent interdisciplinary work in mineralogy and physics or chemistry. Particular emphasis is placed on applications of modern techniques or new theories and models to interpret atomic structures and physical or chemical properties of minerals. Some subjects of interest are: -Relationships between atomic structure and crystalline state (structures of various states, crystal energies, crystal growth, thermodynamic studies, phase transformations, solid solution, exsolution phenomena, etc.) -General solid state spectroscopy (ultraviolet, visible, infrared, Raman, ESCA, luminescence, X-ray, electron paramagnetic resonance, nuclear magnetic resonance, gamma ray resonance, etc.) -Experimental and theoretical analysis of chemical bonding in minerals (application of crystal field, molecular orbital, band theories, etc.) -Physical properties (magnetic, mechanical, electric, optical, thermodynamic, etc.) -Relations between thermal expansion, compressibility, elastic constants, and fundamental properties of atomic structure, particularly as applied to geophysical problems -Electron microscopy in support of physical and chemical studies -Computational methods in the study of the structure and properties of minerals -Mineral surfaces (experimental methods, structure and properties)