The effect of differences in coordination on ordering polyvalent cations in close-packed structures; the crystal structure of arakiite and comparison with hematolite

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Authors:Cooper, Mark A.; Hawthorne, Frank C.
Author Affiliations:Primary:
University of Manitoba, Department of Geological Sciences, Winnipeg, MB, Canada
Volume Title:Canadian Mineralogist
Source:The Canadian Mineralogist, Vol.37(Part 6), p.1471-1482. Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada. ISSN: 0008-4476
Publication Date:1999
Note:In English with French summary. 10 refs.; illus., incl. 6 tables
Summary:The crystal structure of arakiite, (Zn,Mn2+)(Mn2+,Mg)12(Fe3+,Al)2 (As3+O3)(As5+O4)2(OH)23, (space group Cc, a 14.236, b 8.206, c 24.225 Å, β 93.52°, V 2824.0 Å3, Z = 4) has been refined to R 5.6%. There are 18 crystallographically distinct cation sites; the site occupancies have been assigned on the basis of refined site-scattering values, observed stereochemistry and EPMA results. Arakiite has a close-packed packet structure with five anion layers that stack along the c axis, with general compositions ([]7(Tφ410], [[]3(TO410], [[]4M3(TO310], [[]6M1(TO49] and [[]M6φ14]. Four of these layers are topologically identical to the corresponding layers in hematolite; the fifth layer differs between the two structures, with arakiite [[]7(Tφ410] and hematolite [[]614]. [R.A.H.]
Sections:Crystal structure
Subsections:Specific structures: non-silicates
Subjects:Arsenates; Atomic packing; Cations; Coordination; Correlation; Crystal chemistry; Crystal structure; Electron probe data; Order-disorder; Valency; Europe; Scandinavia; Sweden; Varmland Sweden; Western Europe; Arakiite; Hematolite; Langban Sweden
Abstract Numbers:00M/3624
Record ID:2000050464
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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