Fluorapophyllite-(Cs), CsCa4(Si8O20)F(H2O)8, a new apophyllite-group mineral from the Darai-Pioz Massif, Tien-Shan, northern Tajikistan

IF 1.1 4区地球科学 Q3 MINERALOGY

Canadian Mineralogist Pub Date : 2019-11-30 DOI:10.3749/canmin.1900038

A. Agakhanov, L. Pautov, A. Kasatkin, V. Y. Karpenko, E. Sokolova, Maxwell C. Day, F. Hawthorne, V. A. Muftakhov, I. Pekov, F. Cámara, S. Britvin

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引用次数: 2

Abstract

Abstract: Fluorapophyllite-(Cs) (IMA 2018-108a), ideally CsCa4(Si8O20)F(H2O)8, is an apophyllite-group mineral from the moraine of the Darai‐Pioz glacier, Tien‐Shan, Northern Tajikistan. Associated minerals are quartz, pectolite, baratovite, aegirine, leucosphenite, pyrochlore, neptunite, fluorapophyllite-(K), reedmergnerite. Fluorapophyllite-(Cs) is a hydrothermal mineral. It is colourless, it has a vitreous luster and a white streak. Cleavage is perfect, it is brittle and has a stepped fracture. Mohs hardness is 4.5–5. Dmeas. = 2.54(2) g/cm3, Dcalc. = 2.513 g/cm3. Fluorapophyllite(Cs) is unixial (+) with refractive indices (λ = 589 nm) ω = 1.540(2), ε = 1.544(2). It is non-pleochroic. Chemical analysis by electron microprobe gave SiO2 48.78, Al2O3 0.05, CaO 22.69, Cs2O 10.71, K2O 1.13, Na2O 0.04, F 1.86, H2Ocalc. 14.61, –O=F2 –0.78, sum 99.09 wt.%, H2O was calculated from crystal-structure analysis. The empirical formula based on 29 (O + F) apfu, H2O = 8 pfu, is (Cs0.75K0.24)Σ0.99(Ca3.99Na0.01)Σ4(Si8.01Al0.01)Σ8.02 O20.03F0.97(H2O)8, Z = 2. The simplified formula is (Cs,K)(Ca,Na)4(Si,Al)8O20F(H2O)8. Fluorapophyllite-(Cs) is tetragonal, space group P4/mnc, a 9.060(6), c 15.741(11) Å, V 1292.10(19) Å3. The crystal structure has been refined to R1 = 4.31% based on 498 unique (Fo > 4σF) reflections. In the crystal structure of fluorapophyllite-(Cs), there is one [4]T site occupied solely by Si, = 1.615 Å. SiO4 tetrahedra link to form a (Si8O20)8– sheet perpendicular to [001]. Between the Si–O sheets, there are two cation sites: A and B. The A site is coordinated by eight H2O groups [O(4) site], A–O(4) = 3.152(4) Å; the A site contains Cs0.75K0.24o0.01, ideally Cs apfu. The Cs–O bondlength of 3.152 Å is definitely larger than the K–O bondlength of 2.966–2.971 Å in fluorapophyllite-(K), KCa4(Si8O20)F(H2O)8. The [7]B site contains Ca3.99Na0.01, ideally Ca4 apfu; = 2.420 Å (φ = O, F, H2O). The Si–O sheets connect via A and B polyhedra and hydrogen bonding; two H atoms have been included in the refinement. Fluorapophyllite-(Cs) is isostructural with fluorapophyllite-(K). Fluorapophyllite-(Cs) is a

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塔吉克斯坦北部天山Darai Pioz地块的一种新的脱叶石群矿物——氟脱叶石-（Cs），CsCa4（Si8O20）F（H2O）8

摘要：氟叶绿石-（Cs）（IMA 2018-108a），理想情况下为CsCa4（Si8O20）F（H2O）8，是塔吉克斯坦北部天山Darai‐Pioz冰川冰碛中的一种叶绿石群矿物。伴生矿物有石英、果胶岩、白榴石、赤铁矿、隐霞石、烧绿石、镎石、萤石-（K）、芦苇镁石。萤石是一种热液矿物。它无色，有玻璃光泽和白色条纹。解理是完美的，它很脆，有阶梯状断裂。莫氏硬度为4.5–5。D测量=2.54（2）g/cm3，Dcalc.=2.513克/立方厘米。萤石（Cs）为单轴（+），折射率（λ=589nm）ω=1.540（2），ε=1.544（2）。电子探针化学分析得到SiO2 48.78，Al2O3 0.05，CaO 22.69，Cs2O 10.71，K2O 1.13，Na2O 0.04，F 1.86，H2Ocalc。14.61，–O=F2–0.78，总和99.09 wt.%，H2O通过晶体结构分析计算。基于29（O+F）apfu，H2O=8pfu的经验公式为（Cs0.75K0.24）∑0.99（Ca3.99Na0.01）∑4（Si8.01Al0.01）∑8.02 O20.03F0.97（H2O）8，Z=2。简化公式为（Cs，K）（Ca，Na）4（Si，Al）8O20F（H2O）8。萤石-（Cs）是四方晶系，空间群P4/mnc，a 9.060（6），c 15.741（11）Å，V 1292.10（19）Å3。基于498个独特的（Fo>4σF）反射，晶体结构被细化为R1=4.31%。在荧光体-（Cs）的晶体结构中，有一个[4]T位点仅被Si占据，=1.615Å。SiO4四面体连接形成垂直于[001]的（Si8O20）8–片。在Si–O片之间，有两个阳离子位点：A和B。A位点由八个H2O基团[O（4）位点]配位，A–O（4）=3.152（4）Å；A位点含有Cs0.75K0.24o0.01，理想情况下为Cs-apfu。3.152Å的Cs–O键长肯定大于氟叶绿柱石-（K），KCa4（Si8O20）F（H2O）8中2.966–2.971Å的K–O键长度。[7]B位点含有Ca3.99Na0.01，理想情况下为Ca4-apfu；=2.420Å（φ=O，F，H2O）。Si–O片通过A和B多面体和氢键连接；两个H原子已经被包括在细化中。萤石-（Cs）与萤石-（K）是同结构的。萤石-（Cs）是一种

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来源期刊

Canadian Mineralogist 地学-矿物学

CiteScore

2.20

自引率

22.20%

发文量

审稿时长

4-8 weeks

期刊介绍： Since 1962, The Canadian Mineralogist has published papers dealing with all aspects of mineralogy, crystallography, petrology, economic geology, geochemistry, and applied mineralogy.