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Crystal structures and isotypism of the iron(III) arsenate kamarizaite and the iron(III) phosphate tinticite

Uwe Kolitsch, Christian L. Lengauer and Gerald Giester
Crystal structures and isotypism of the iron(III) arsenate kamarizaite and the iron(III) phosphate tinticite
European Journal of Mineralogy (August 2015) 28 (1): 71-81


The crystal structures of the secondary ferric iron minerals kamarizaite, Fe (sub 3) (super 3+) (AsO (sub 4) ) (sub 2) (OH) (sub 3) . 3H (sub 2) O, and tinticite, Fe (sub 3) (super 3+) (PO (sub 4) ) (sub 2) (OH) (sub 3) . 3H (sub 2) O, for which highly contradictory data on crystal symmetry were reported, were studied by a combination of single-crystal X-ray diffraction and Rietveld refinement (supplemented by chemical analyses and thermogravimetry), using type material of both species and additional samples from several other localities, including the type localities. The previously unknown crystal structure of kamarizaite was determined from single-crystal intensity data (MoKalpha , 293 K, R(F) = 2.91 %; all H atoms detected) using a sample from the Le Mazet vein, Echassieres, Auvergne, France. The mineral is triclinic, space group P-1 (no. 2), with a = 7.671(2), b = 8.040(2), c = 10.180(2) Aa, alpha = 68.31(3), beta = 75.35(3), gamma = 63.52(3) degrees , V = 519.3(2) Aa (super 3) , Z = 1. Rietveld analyses of fine-grained kamarizaite collected underground at two different spots in Lavrion, Greece (Hilarion and Jean Baptiste areas) confirmed the structure model. Rietveld analyses of fine-grained tinticite from Tintic, Utah (USA), Bruguers (Spain) and Weckersdorf (Germany) demonstrate that kamarizaite and tinticite are triclinic and isotypic. A previously published structure model for tinticite, as well as the originally reported orthorhombic symmetry for kamarizaite, are shown to be incorrect. Refined unit-cell parameters of a cotype tinticite specimen from Tintic are: a=7.647(1), b= 7.958(1), c =9.987(1)Aa, alpha = 67.90(1), beta = 76.10(1), gamma = 64.10(1) degrees , V = 504.4(2) Aa (super 3) . Bruguers and Weckersdorf tinticite have very similar parameters. The common atomic arrangement is characterised by three unique, octahedrally coordinated Fe sites (which may be partially replaced by minor Al), two unique tetrahedrally coordinated T (As or P) sites, eight O, three O (sub h) , three O (sub w) and nine H sites. The topology features zig-zag chains along [1-10] of dimers built of two edge-sharing FeO (sub 6) octahedra corner-linked by a third FeO (sub 6) octahedron. The chains are corner-linked by the TO (sub 4) tetrahedra thus establishing a mixed octahedral-tetrahedral framework with a T:Fe ratio of 0.67, a pronounced layered arrangement parallel to (001) and narrow channels along [010]. Medium-strong to weak hydrogen-bonds provide additional strengthening of the structure. The topology is closely related to that of the recently described, triclinic aluminium phosphate afmite.

ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 28
Serial Issue: 1
Title: Crystal structures and isotypism of the iron(III) arsenate kamarizaite and the iron(III) phosphate tinticite
Affiliation: Naturhistorisches Museum, Mineralogisch-Petrographische Abtheilung, Vienna, Austria
Pages: 71-81
Published: 20150817
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 33
Accession Number: 2015-089144
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 8 tables
N37°43'00" - N37°43'00", E24°01'60" - E24°01'60"
N50°37'22" - N50°37'22", E11°55'31" - E11°55'31"
N41°19'00" - N41°19'00", E01°58'00" - E01°58'00"
N39°57'00" - N39°57'00", W112°04'00" - W112°04'00"
Secondary Affiliation: Universitaet Wien, AUT, Austria
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201538
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