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

Biagion, Cristian, (författare)
Università di Pisa, Italy
Bosi, Ferdinando, (författare)
Sapienza Università di Roma, Italy
Hålenius, Ulf, (författare)
Naturhistoriska riksmuseet, Enheten för geovetenskap
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Pasero, Marco, (författare)
Università di Pisa, Italy
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Ingår i: American Mineralogist. - 0003-004X .- 1945-3027. ; 102, s. 1981-1986
  • Tidskriftsartikel (refereegranskat)
Abstract Ämnesord
  • <p>The crystal structure of turneaureite, ideally Ca<sub>5</sub>(AsO<sub>4</sub>)<sub>3</sub>Cl, was studied using a specimen from the Brattfors mine, Nordmark, Värmland, Sweden, by means of single-crystal X-ray diffraction data. The structure was refinedto R1 = 0.017 on the basis of 716 unique reflectios with F<sub>o</sub> &gt; 4σ(F<sub>o</sub>) in the <em>P</em>6<sub>3</sub>/<em>m</em> space group, with unit-cell parameters <em>a</em> = 9.9218(3), <em>c </em>= 6.8638(2) Å, V = 585.16(4) Å<sup>3</sup>. The chemical composition of the sample, determined by electron-microprobe analysis, is (in wt%; average of 10 spot analyses): SO<sub>3</sub> 0.22, P<sub>2</sub>O<sub>5</sub> 0.20, V<sub>2</sub>O<sub>5</sub> 0.01, As<sub>2</sub>O<sub>5</sub> 51.76, SiO<sub>2</sub> 0.06, CaO 41.39, MnO 1.89, SrO 0.12, BaO 0.52, PbO 0.10, Na2O 0.02, F 0.32, Cl 2.56, H<sub>2</sub>O<sub>calc</sub> 0.58, O(≡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</sub>Mn<sub>0.17</sub>Ba<sub>0.02</sub>Sr<sub>0.01</sub>)∑<sub>5.02</sub> (As<sub>2.94</sub>P<sub>0.02</sub>S<sub>0.02</sub>Si<sub>0.01</sub>)<sub>∑2.99</sub>O<sub>12</sub>[Cl<sub>0.47</sub>(OH)<sub>0.42</sub>F<sub>0.11</sub>]<sub>∑1.00</sub>.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</sub> 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 filledanion 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.</p>


NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geokemi (hsv//swe)
NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geochemistry (hsv//eng)


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