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The crystal structure of turneaureite, Ca (sub 5) (AsO (sub 4) ) (sub 3) Cl, the arsenate analog of chlorapatite, and its relationships with the arsenate apatites johnbaumite and svabite

Cristian Biagioni, Ferdinando Bosi, Ulf Halenius and Marco Pasero
The crystal structure of turneaureite, Ca (sub 5) (AsO (sub 4) ) (sub 3) Cl, the arsenate analog of chlorapatite, and its relationships with the arsenate apatites johnbaumite and svabite
American Mineralogist (October 2017) 102 (10): 1981-1986

Abstract

The crystal structure of turneaureite, ideally Ca (sub 5) (AsO (sub 4) ) (sub 3) Cl, was studied using a specimen from the Brattfors mine, Nordmark, Varmland, Sweden, by means of single-crystal X-ray diffraction data. The structure was refined to R (sub 1) = 0.017 on the basis of 716 unique reflections with F (sub o) > 4sigma (F (sub o) ) in the P6 (sub 3) /m space group, with unit-cell parameters a = 9.9218(3), c = 6.8638(2) A, V = 585.16(4) A (super 3) The chemical composition of the sample, determined by electron-microprobe analysis, is (in wt%; average of 10 spot analyses): SO (sub 3) 0.22, P (sub 2) O (sub 5) 0.20, V (sub 2) O (sub 5) 0.01, As (sub 2) O (sub 5) 51.76, SiO (sub 2) 0.06, CaO 41.39, MnO 1.89, SrO 0.12, BaO 0.52, PbO 0.10, Na (sub 2) O 0.02, F 0.32, Cl 2.56, H (sub 2) O (sub calc) 0.58, O( identical with F+Cl) -0.71, total 99.04. On the basis of 13 anions per formula unit, the empirical formula corresponds to (Ca (sub 4.82) Mn (sub 0.17) Ba (sub 0.02) Sr (sub 0.01) ) (sub Sigma ) (sub 5.02) (As (sub 2.94) P (sub 0.02) S (sub 0.02) Si (sub 0.01) ) (sub Sigma ) (sub 2.99) O (sub 12) [Cl (sub 0.47) (OH) (sub 0.42) F (sub 0.11) ] (sub Sigma ) (sub 1.00) . Turneaureite is topologically similar to the other members of the apatite supergroup: columns of face-sharing M1 polyhedra running along c are connected through TO (sub 4) tetrahedra with channels hosting M2 cations and X anions. Owing to its particular chemical composition, the studied turneaureite can be considered as a ternary calcium arsenate apatite; consequently it has several partially filled anion sites within the anion columns. Polarized single-crystal FTIR spectra of the studied sample indicate stronger hydrogen bonding and less diverse short-range atom arrangements around (OH) groups in turneaureite as compared to the related minerals johnbaumite and svabite. An accurate knowledge of the atomic arrangement of this apatite-remediation mineral represents an improvement in our understanding of minerals able to sequester and stabilize heavy metals such as arsenic in polluted areas.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 102
Serial Issue: 10
Title: The crystal structure of turneaureite, Ca (sub 5) (AsO (sub 4) ) (sub 3) Cl, the arsenate analog of chlorapatite, and its relationships with the arsenate apatites johnbaumite and svabite
Affiliation: Universita di Pisa, Dipartimento di Scienze della Terra, Pisa, Italy
Pages: 1981-1986
Published: 201710
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 29
Accession Number: 2017-090024
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables
N58°52'60" - N61°02'60", E01°42'00" - E14°30'00"
Secondary Affiliation: Sapienza Universita di Roma, ITA, ItalyCNR, Istituto di Geoscienze e Georisorse, ITA, ItalySwedish Museum of Natural History, SWE, Sweden
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201747
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