Cacoxenite—a Complex Phosphate with a Modular Structure

IF 0.8 4区地球科学 Q3 GEOLOGY

Geology of Ore Deposits Pub Date : 2024-02-07 DOI:10.1134/s1075701523070024

M. S. Avdontceva, S. V. Krivovichev, M. G. Krzhizhanovskaya, V. N. Bocharov, N. S. Vlasenko, D. V. Spiridonova

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Abstract

The crystal chemical peculiarities of cacoxenite from the Těškov quarry (Bohemia, Czech Republic) are studied using single crystal X-ray analysis and thermal X-ray analysis, electron-microprobe analysis, and infrared (IR) and Raman spectroscopy. The crystal structure of cacoxenite (hexagonal system, sp. gr. P6₃/m, a = 27.5677(4) Å, c = 10.5364(3) Å, V = 6934.64(16) Å³) is refined to R₁ = 0.052 by 4637 independent reflections. The crystal structure is based on two independent structural blocks, which form an open-framework (the minimum free pore diameter is 15.1 Å). The crystal structure of cacoxenite is stable up to 190°C. The empirical formula of the mineral (based on 17 P atoms) is (\({\text{Fe}}_{{19.98}}^{{3 + }}\)Al_4.97)_Σ24.95O₆(PO₄)₁₇(OH_8.52Cl_3.48)_Σ12(H₂O)₂₄⋅ nH₂O (n ∼ 50). The most intense bands of IR and Raman spectra in a range from 400 to 1200 cm^–1 correspond to stretching and bending vibration modes of the phosphate groups. The presence of water in the structure is confirmed by the presence of an intense band in the IR spectrum in the area of 1624 cm^–1 (O–H vibrations), as well as the absorption band with maximum of 3357 cm^–1, which corresponds to stretching vibrations of the Fe(Al)–OH bond and H₂O molecules. The calculation of structural complexity of cacoxenite for the framework without H-corrections and with the addition of framework-related H-positions shows a very complex structure of the mineral (2312.464 bit/cell).

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孔雀石--一种具有模块化结构的复合磷酸盐

摘要利用单晶 X 射线分析和热 X 射线分析、电子探针分析、红外光谱和拉曼光谱，研究了 Těškov 采石场（捷克共和国波希米亚）出产的埃克森石的晶体化学特性。通过 4637 次独立反射，将可可碱石（六方体系，sp. gr. P63/m，a = 27.5677(4) Å，c = 10.5364(3) Å，V = 6934.64(16) Å3）的晶体结构细化为 R1 = 0.052。该晶体结构基于两个独立的结构块，它们形成了一个开放框架（最小自由孔径为 15.1 Å）。可可碱石的晶体结构在 190°C 以下都很稳定。该矿物的经验公式（基于 17 个 P 原子）为 (\({\{Fe}}_{{19.98}}^{{3 + }}\)Al4.97)Σ24.95O6(PO4)17(OH8.52Cl3.48)Σ12(H2O)24⋅ nH2O (n ∼ 50)。红外光谱和拉曼光谱中 400 至 1200 cm-1 范围内最强烈的波段对应于磷酸基团的伸展和弯曲振动模式。在红外光谱中，1624 cm-1（O-H 振动）区域存在一条强波段，以及最大值为 3357 cm-1 的吸收波段（对应于 Fe(Al)-OH 键和 H2O 分子的伸缩振动）证实了结构中水的存在。在不进行 H 校正和添加与框架相关的 H 位置的情况下，对卡考氙石框架结构复杂性的计算显示，该矿物的结构非常复杂（2312.464 位/单元）。

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来源期刊

Geology of Ore Deposits 地学-地质学

CiteScore

1.10

自引率

14.30%

发文量

审稿时长

6-12 weeks

期刊介绍： Geology of Ore Deposits is a periodical covering the topic of metallic and nonmetallic mineral deposits, their formation conditions, and spatial and temporal distribution. The journal publishes original scientific articles and reviews on a wide range of problems in theoretical and applied geology. The journal focuses on the following problems: deep geological structure and geodynamic environment of ore formation; distribution pattern of metallogenic zones and mineral deposits; geology and formation environment of large and unique metallic and nonmetallic deposits; mineralogy of metallic and nonmetallic deposits; physicochemical and isotopic characteristics and geochemical environment of ore deposition; evolution of ore-forming systems; radiogeology and radioecology, economic problems in exploring, developing, and mining of ore commodities.