Three specimens of galkhaite from the Getchell mine (G), Nevada, USA; the Gal-Khaya As-Hg-Sb deposit (Gk), Yakutia, Russia; and Signols (S), Piedmont, Italy, have been fully characterized through single-crystal X-ray diffraction and electronmicroprobe analyses. Chemical data indicate the formulae [(Hg<inf>4.61</inf>Zn<inf>0.38</inf>Fe<inf>0.04</inf>)<inf>Σ5.03</inf>(Cu<inf>1.03</inf>Ag<inf>0.04</inf>)<inf>Σ1.07</inf>]<inf>Σ6.10</inf>(Cs<inf>0.76</inf>Tl<inf>0.20</inf>)<inf>Σ0.96</inf>(AS<inf>3.81</inf>Sb<inf>0.04</inf>)<inf>Σ3.85</inf>S<inf>12.06</inf> (G), [(Hg<inf>4.66</inf>Zn<inf>0.32</inf>)<inf>Σ4.98</inf>(Cu<inf>0.55</inf>Ag<inf>0.45</inf>)<inf>Σ1.00</inf>]<inf>Σ5.98</inf>(Cs<inf>0.74</inf>Tl<inf>0.06</inf>(As<inf>3.42</inf>Sb<inf>0.56</inf>)<inf>Σ3.98</inf>S<inf>12.05</inf> (Gk), and [(Hg<inf>4.10</inf>Zn<inf>0.85</inf>)<inf>Σ4.95</inf>(Cu<inf>0.89</inf>Ag<inf>0.16</inf>)<inf>Σ1.05</inf>]<inf>Σ6.00</inf>Cs<inf>0.95</inf>As<inf>3.64</inf>Sb<inf>0.16</inf>)Σ3.80 S<inf>12.19</inf> (S). Unit-cell parameters are a 10.405(3) Å (G), 10.443(1) Å (Gk), and 10.332(2) Å (S), space group I4¯3m. The crystal structure of the three specimens has been solved to R<inf>1</inf> = 0.029 (G), 0.028 (Gk), and 0.031 (S). It is a three-dimensional framework of HgS<inf>4</inf> and AsS<inf>3</inf> polyhedra, with Cs hosted in large 12-fold coordinated cavities. The introduction of Cs<sup>+</sup>, as well as minor Tl<sup>+</sup> , at these structural positions requires the replacement of Hg<sup>2+</sup> by Cu<sup>+</sup> . The mixed site occupancy at the Hg site of galkhaite is a case of valency-imposed double site-occupancy. Consequently, the idealized chemical formula of galkhaite can be written as (Hg<inf>5</inf>Cu)CsAs<inf>4</inf>S<inf>12</inf>. Taking into account the possible existence of vacancy in the structural cavities, the formula can be generalized as (Hg<inf>5+x</inf>Cu<inf>1-x</inf>)<inf>Σ6</inf>Cs<inf>1-x</inf>As<inf>4</inf>S<inf>12</inf> (x ≈ 0).

Crystal chemistry of mercury sulfosalts - Galkhaite, (Hg5+xCu1-x)Cs1-xAs4S12 (x ≈ 0): Crystal structure and revision of the chemical formula

BIAGIONI, CRISTIAN;
2014-01-01

Abstract

Three specimens of galkhaite from the Getchell mine (G), Nevada, USA; the Gal-Khaya As-Hg-Sb deposit (Gk), Yakutia, Russia; and Signols (S), Piedmont, Italy, have been fully characterized through single-crystal X-ray diffraction and electronmicroprobe analyses. Chemical data indicate the formulae [(Hg4.61Zn0.38Fe0.04)Σ5.03(Cu1.03Ag0.04)Σ1.07]Σ6.10(Cs0.76Tl0.20)Σ0.96(AS3.81Sb0.04)Σ3.85S12.06 (G), [(Hg4.66Zn0.32)Σ4.98(Cu0.55Ag0.45)Σ1.00]Σ5.98(Cs0.74Tl0.06(As3.42Sb0.56)Σ3.98S12.05 (Gk), and [(Hg4.10Zn0.85)Σ4.95(Cu0.89Ag0.16)Σ1.05]Σ6.00Cs0.95As3.64Sb0.16)Σ3.80 S12.19 (S). Unit-cell parameters are a 10.405(3) Å (G), 10.443(1) Å (Gk), and 10.332(2) Å (S), space group I4¯3m. The crystal structure of the three specimens has been solved to R1 = 0.029 (G), 0.028 (Gk), and 0.031 (S). It is a three-dimensional framework of HgS4 and AsS3 polyhedra, with Cs hosted in large 12-fold coordinated cavities. The introduction of Cs+, as well as minor Tl+ , at these structural positions requires the replacement of Hg2+ by Cu+ . The mixed site occupancy at the Hg site of galkhaite is a case of valency-imposed double site-occupancy. Consequently, the idealized chemical formula of galkhaite can be written as (Hg5Cu)CsAs4S12. Taking into account the possible existence of vacancy in the structural cavities, the formula can be generalized as (Hg5+xCu1-x)Σ6Cs1-xAs4S12 (x ≈ 0).
2014
Biagioni, Cristian; Bindi, Luca; Zaccarini, Federica
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/815733
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