New crystal-chemical data on zincoberaunite from Krásno near Horní Slavkov (Czech Republic)

IF 1.1 4区地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS

Journal of Geosciences Pub Date : 2020-04-12 DOI:10.3190/jgeosci.296

J. Tvrdý, J. Plášil, R. Škoda

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引用次数: 4

Abstract

A study of zincoberaunite from Krásno near Horní Slavkov (Czech Republic) provided new chemical and structural data of this rare member of the beraunite group. The studied material is monoclinic, space group C2/c, with a = 20.3440(19) Å, b = 5.1507(3) Å, c = 19.1361(15) Å, β = 93.568(8)°, V = 2001.3(3) Å3, Z = 4. Based on refined site occupancies and bond-valence considerations, the structural formula is (Zn0.81Al0.19)(OH)2(Fe0.61Al0.39)(OH)2(H2O)2(Fe1.52Al0.48)(H2O)2(Fe1.72Al0.28) (OH)(PO4)3.83(AsO4)0.17(H2O)2. Electron-microprobe analyses support the obtained results. However, keeping the same cation occupancy at the M2–M4 sites, the ratio of Al3+ to Me2+ at the M1 site requires the presence of divalent cations as follows: (Zn0.57Fe0.24Al0.19)Σ1.00(Fe3.85Al1.15)Σ5.00[(PO4)3.89(AsO4)0.10(SiO4)0.01]Σ4.00[(OH)4.59F0.24 O0.17]Σ5.00(OH2)4.00·2H2O. Individual prismatic zincoberaunite crystals exhibit a chemical zonation manifested by increasing Fe and decreasing Zn and Al contents from cores to rims. The mineral composition is close to the Zn–Al-rich members of the beraunite group known from the same locality, but in this case, dominant occupancy of Zn at the M1 site was confirmed. With its increased aluminium content, zincoberaunite from Krásno differs significantly from the holotype specimen described from Hagendorf South pegmatite in Germany. The most prominent Raman bands are in good agreement with data published for related members of the beraunite group. Structure refinement (R = 3.56 % for 1906 observed unique reflections) revealed three different types of OH or H2O, which play distinct role in structure bonding.

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HorníSlavkov附近Krásno锌钴酸盐的新晶体化学数据（捷克共和国）

对HorníSlavkov（捷克共和国）附近Krásno的锌硼镁石的研究提供了这种罕见的硼镁石群成员的新化学和结构数据。所研究的材料是单斜的，空间群C2/c，a=20.3440（19）Å，b=5.1507（3）Å、c=19.1361（15）Å和β=93.568（8）°，V=2001.3（3）å3，Z=4。基于精细的位点占用和键价考虑，结构式为（Zn0.81Al0.19）（OH）2（Fe0.61Al0.39）。电子探针分析支持所获得的结果。然而，在M2–M4位点保持相同的阳离子占有率，M1位点的Al3+与Me2+之比需要二价阳离子的存在，如下所示：（Zn0.57Fe0.24Al0.19）∑1.00（Fe3.85Al1.15）∑5.00[（PO4）3.89（AsO4）0.10（SiO4）0.01]∑4.00[（OH）4.59F0.24O0.17]∑5.00（OH2）4.00·2H2O。单个棱柱状锌钴石晶体表现出化学分带现象，表现为从核心到边缘的Fe增加和Zn和Al含量减少。矿物成分接近同一地区已知的富含锌-铝的紫苏岩群成员，但在这种情况下，证实了锌在M1位点的主要占有率。随着铝含量的增加，Krásno的锌钴矿与德国Hagendorf South伟晶岩的正模标本有很大不同。最突出的拉曼光谱带与发表的紫苏属相关成员的数据非常一致。结构细化（1906次观察到的独特反射的R=3.56%）揭示了三种不同类型的OH或H2O，它们在结构键合中起着不同的作用。

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来源期刊

Journal of Geosciences GEOSCIENCES, MULTIDISCIPLINARY-MINERALOGY

CiteScore

2.30

自引率

7.10%

发文量

审稿时长

>12 weeks

期刊介绍： The Journal of Geosciences is an international peer-reviewed journal published by the Czech Geological Society with support from the Czech Geological Survey. It accepts high-quality original research or review papers dealing with all aspects of the nature and origin of igneous and metamorphic rocks. The Journal focuses, mainly but not exclusively, on: -Process-oriented regional studies of igneous and metamorphic complexes- Research in structural geology and tectonics- Igneous and metamorphic petrology- Mineral chemistry and mineralogy- Major- and trace-element geochemistry, isotope geochemistry- Dating igneous activity and metamorphic events- Experimental petrology and mineralogy- Theoretical models of igneous and metamorphic processes- Mineralizing processes and mineral deposits. All the papers are written in English, even though they may be accompanied by an additional Czech abstract. Each contribution is a subject to peer review by at least two independent reviewers, typically at least one from abroad. The Journal appears 2 to 4 times a year. Formally it is divided in annual volumes, each of them including 4 issues.