Rotemite, Ca4Cr2(OH)12Cl2·4h2o -水矾石和弗里德尔盐的三角铬类似物-以色列Hatrurim杂岩的新矿物

IF 5.8 2区地球科学 Q2 CHEMISTRY, PHYSICAL

Applied Clay Science Pub Date : 2025-10-03 DOI:10.1016/j.clay.2025.108002

Katarzyna Skrzyńska , Harald Müller , Rafał Juroszek , Biljana Krüger , Georgia Cametti , Anna Pakhomova , Irina Galuskina , Yevgeny Vapnik , Krzysztof Woźniak , Evgeny Galuskin

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引用次数: 0

摘要

铁矾石（Ca4Cr2(OH)12Cl2·4H2O）是一种新发现的矿物，是水滑石超群中第一个含铬的水矾土族成员。这种新矿物是一种三棱铬类似物，类似于水矾土和它的合成对应物弗里德尔盐，代表了一大家族的新型层状/层状双氢氧化物（LDH）化合物。这项工作提出了LDH家族中Ca， Cr-bearing化合物的第一个综合研究。Rotemite是在以色列Hatrurim杂岩的热变质岩中发现的。它形成微小的六角形片状晶体，呈现淡蓝紫色（日光）到粉紫色（人造光），这取决于照明的类型。条纹呈浅紫色。光学上，铁铁矿呈负单轴，ω = 1.565(2), ε = 1.544(2) （λ = 589 nm）。它的硬度在莫氏硬度2.5-3之间。晶体在{0001}上表现出完美的解理。电子探针分析得到(Ca3.94Sr0.01)∑3.95(Cr3+1.47Al0.52Fe3+0.05)∑2.04(OH)12[Cl1.68(OH)0.32(SO4)0.01]∑2.01·4H2O的经验公式。根据经验公式和单晶x射线衍射数据得到的单胞参数计算密度为2.18 g/cm3。单晶x射线衍射测量表明，铁铁矿为6层多晶型，具有三角形对称（R3¯c），胞元参数为a = 5.7944(2) Å， c = 46.69(4) Å， V = 1357.7（10） Å3。最终的结构模型收敛于R1 = 0.0866。该结构由水钙石型层[Ca4(Cr,Al)2(OH)12(H2O)4]2+和插层Cl−离子组成。铁矾的拉曼光谱在~ 525 cm−1处有一个突出的带，这是LDH化合物的典型特征。偏振拉曼光谱表明，OH在3441 ~ 3442 cm−1和3609 ~ 3612 cm−1处的拉伸振动信号与入射激光束的偏振方向密切相关。这分别表明水分子的有序排列和氢氧根键在水钙石层中的垂直排列。讨论了铁铁矿和其他含Cr3+矿物的来源，以及[Cr(OH)6]3−阴离子在其形成中的可能作用。

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Rotemite, Ca4Cr2(OH)12Cl2·4 H2O – the trigonal chromium analog of hydrocalumite and Friedel’s salt – a new mineral from the Hatrurim Complex, Israel

Rotemite, Ca₄Cr₂(OH)₁₂Cl₂·4H₂O, is a newly discovered mineral and the first Cr-bearing member of the hydrocalumite group within the hydrotalcite supergroup. The new mineral is a trigonal chromium analog of both hydrocalumite and its synthetic counterpart, Friedel's salt, representing a large family of novel compounds of lamellar/layered double hydroxides (LDH). This work presents the first comprehensive study of a Ca, Cr-bearing compound within the LDH family. Rotemite was discovered in pyrometamorphic rocks of the Hatrurim Complex, Israel. It forms tiny hexagonal platelet-shaped crystals that appear pale bluish-violet (daylight) to pinkish-violet (artificial light), depending on the type of illumination. The streak is pale light-purple. Optically, rotemite is negatively uniaxial with ω = 1.565(2), ε = 1.544(2) (λ = 589 nm). It has a hardness of 2.5–3 on the Mohs scale. The crystals exhibit perfect cleavage on {0001}. The electron microprobe analyses indicated the empirical formula of (Ca_3.94Sr_0.01)_∑3.95(Cr³⁺_1.47Al_0.52Fe³⁺_0.05)_∑2.04(OH)₁₂[Cl_1.68(OH)_0.32(SO₄)_0.01]_∑2.01·4H₂O.

The calculated density, based on the empirical formula and unit cell parameters obtained from single-crystal X-ray diffraction data, is 2.18 g/cm³. Single-crystal X-ray diffraction measurements have revealed that rotemite represents a 6-layered polytype with trigonal symmetry (

R \bar{3} c

) and unit cell parameters: a = 5.7944(2) Å, c = 46.69(4) Å, V = 1357.7(10) Å³. The final structural model converged to R₁ = 0.0866. The structure consists of hydrocalumite-type layers [Ca₄(Cr,Al)₂(OH)₁₂(H₂O)₄]²⁺ with intercalated Cl⁻ ions. Raman spectra of rotemite are characterized by a prominent band at ∼525 cm⁻¹, typical of LDH compounds. Polarized Raman spectroscopy revealed that signals from OH stretching vibrations at 3441–3442 cm⁻¹ and 3609–3612 cm⁻¹ strongly depend on the orientation of the crystal relative to the polarization of the incident laser beam. This indicates both an ordered arrangement of water molecules and a perpendicular arrangement of OH bonds within the hydrocalumite layers, respectively. The origin of rotemite and other Cr³⁺-bearing minerals is discussed, along with the possible role of the [Cr(OH)₆]³⁻ anion in their formation.

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来源期刊

Applied Clay Science 地学-矿物学

CiteScore

10.30

自引率

10.70%

发文量

289

审稿时长

39 days

期刊介绍： Applied Clay Science aims to be an international journal attracting high quality scientific papers on clays and clay minerals, including research papers, reviews, and technical notes. The journal covers typical subjects of Fundamental and Applied Clay Science such as: • Synthesis and purification • Structural, crystallographic and mineralogical properties of clays and clay minerals • Thermal properties of clays and clay minerals • Physico-chemical properties including i) surface and interface properties; ii) thermodynamic properties; iii) mechanical properties • Interaction with water, with polar and apolar molecules • Colloidal properties and rheology • Adsorption, Intercalation, Ionic exchange • Genesis and deposits of clay minerals • Geology and geochemistry of clays • Modification of clays and clay minerals properties by thermal and physical treatments • Modification by chemical treatments with organic and inorganic molecules(organoclays, pillared clays) • Modification by biological microorganisms. etc...