Routhierite, Tl(Cu,Ag)(Hg,Zn)₂(As,Sb)₂S₆

The crystal structure of the mineral routhierite, Tl(Cu,Ag)(Hg,Zn)₂(As,Sb)₂S₆, was solved and refined for the first time by means of single-crystal X-ray diffraction. The crystal structure consists of (Cu,Ag)S₄ and (Hg,Zn)S₄ tetra­hedra, which share corners to form a framework with channels parallel to [001]. These channels contain TlS₆ and (As,Sb)S₃ polyhedra that share corners and edges with the tetra­hedra. The crystal-chemical relationships with other Tl-Hg sulfosalts are outlined. The structure determination reported in this study definitively confirms that routhierite and stalderite possess the same crystal structure.

S1. Comment

Routhierite, Tl(Cu,Ag)(Hg,Zn)₂(As,Sb)₂S₆, is a rare mineral first described by Johan et al. (1974) to occur with pierrotite, stibnite, smithite, sphalerite, realgar, orpiment, pyrite and barite in Jas Roux (Hautes-Alpes), France. By means of an X-ray single-crystal study (Weissenberg photographs), these authors pointed out that routhierite is tetragonal (possible space groups I4mm, I42m, I4m2 and I4/mmm, with a = 9.977 (4) Å and c 11.290 Å). However, Johan et al. (1974) were not able to proceed to a crystal structure determination of routhierite at that time. More recently, Graeser et al. (1995) during the structural description of the new Tl sulfosalt mineral stalderite, Tl(Cu,Ag)(Zn,Fe,Hg)₂(As,Sb)₂S₆, pointed out close relationships between stalderite and routhierite. They concluded, indeed, that stalderite represents the Zn equivalent of routhierite. Similar conclusions were reached by Moelo et al. (2008) during a review of sulfosalt systematics. These authors considered routhierite as isotypic with stalderite. To help resolve the concerns relating to the structure of routhierite and to invesitgate the similarity in X-ray patterns for routhierite and stalderite, new crystal structure data for routhierite from its type locality, Jas Roux, are presented.

In the crystal structure of routhierite, (Cu,Ag)S₄ and (Hg,Zn)S₄ tetrahedra share corners to form a framework with channels parallel to [001] (Fig. 1). These channels contain TlS₆ and (As,Sb)S₃ polyhedra that share corners and edges with the tetrahedra (Fig. 2). In detail, the Tl atom is coordinated by (2 + 4) S atoms in the form of an orthorhombic pyramid with a split apex. The mean Tl—S bond distance (i.e. 3.29 Å) is nearly identical to that observed in stalderite (i.e. 3.32 Å; Graeser et al., 1995). The (Cu,Ag) and (Hg,Zn) atoms are surrounded by four S atoms to form slightly distorted tetrahedra. The mean (Cu,Ag)—S distance of 2.43 Å is greater than that observed in stalderite (i.e. 2.36 Å) because of the presence of minor amounts of silver replacing copper at this position. The mean (Hg,Zn)—S distance of 2.51 Å is in fair agreement with those observed for christite, TlHgAsS₃ (i.e. 2.56 Å; Brown & Dickson, 1976), and laffittite, AgHgAsS₃ (i.e. 2.59 Å; Nakai & Appleman, 1983). The shortening of the (Hg,Zn)—S distance in routhierite, however, is due to the minor amount of Zn substituting for Hg. In stalderite, where only Zn is present at this position, the mean bond distance is 2.41 Å (Graser or Graeser et al., 1995). Finally, the (As,Sb) atoms form a trigonal pyramid with three S atoms, with (As,Sb) at the apex [mean (As,Sb)—S = 2.34 Å], as is typical for sulfosalts. It is worth noting that a relatively short Tl—Tl distance of 3.47 Å was observed. This value is similar to the Tl—Tl distance found in elemental thallium (3.40 Å; Wells, 1962) and could indicate some Tl—Tl interactions in the structure. The same feature was also observed in stalderite (Graeser et al., 1995).

The structure determination reported here confirms that routhierite and stalderite possess the same crystal structure.

Related literature

For related literature, see: Johan et al. (1974); Graeser et al. (1995).

S2. Experimental

A crystal was selected from a natural specimen from the type locality (i.e. Jas Roux, France) belonging to the Mineralogical Collection of the Natural History Museum of Florence (catalogue No. 45164/G). A preliminary chemical analysis using energy dispersive spectrometry, performed on the crystal fragment used for the structural study, did not indicate the presence of elements (Z > 9) other than S, Cu, Zn, As, Ag, Sb, Hg and Tl, with a very minor amount of Fe. The chemical composition was then determined using wavelength dispersive analysis (WDS) by means of a Jeol JXA-8600 electron microprobe. Major and minor elements were determined at a 20 kV accelerating voltage and a 40 nA beam current, with a counting time of 10 s. For the WDS analyses the following lines were used: S Kα, Fe Kα, Cu Kα, Zn Kα, As Lα, Ag Lα, Sb Lβ, Hg Lα, Tl Mα. The standards employed were pure metals for Cu, Ag, and Tl; pyrite for Fe and S; cinnabar for Hg; synthetic Sb₂S₃ for Sb; synthetic As₂S₃ for As; and synthetic ZnS for Zn. The routhierite fragment was found to be homogeneous within analytical error. On the basis of 12 atoms, the chemical formula can be written as Tl(Cu_0.65Ag_0.35)_Σ=1.00(Hg_1.70Zn_0.30)_Σ=2.00(As_1.70Sb_0.30)_Σ=2.00S_6.00.

S3. Refinement

The crystal structure of routhierite was solved and refined starting from the atomic coordinates reported for stalderite by Graeser et al. (1995). Convergence was rapidly obtained for an anisotropic model of the structure. In the final cycles, the structure was refined as a racemic twin.

Computing details

Data collection: CrysAlis RED (Oxford Diffraction, 2006); cell refinement: CrysAlis RED (Oxford Diffraction, 2006); data reduction: CrysAlis RED (Oxford Diffraction, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Xtaldraw (Downs & Hall-Wallace, 2003); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

Fig. 1. The crystal structure of routhierite, viewed down [001]. Displacement parameters are drawn at the 50% probability level. The unit-cell is outlined.

Fig. 2. The crystal structure of routhierite, showing the linking of (Cu,Ag)S4 and (Hg,Zn)S4 tetrahedra (in dark green and red, respectively, in the electronic version of the paper), which share corners to form a framework with channels hosting Tl and (As,Sb) atoms. [In the electronic version of the paper, blue, light-green and yellow spheres indicate Tl, As and S atoms, respectively.] The unit-cell is outlined.

Routhierite

Crystal data

Tl(Cu·Ag)(Hg·Zn)2(As·Sb)2S6	Dx = 5.895 Mg m^−3
Mr = 1000.29	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I42m	Cell parameters from 40 reflections
Hall symbol: I -4 2	θ = 10.4–25.1°
a = 9.9821 (11) Å	µ = 46.48 mm^−1
c = 11.3122 (12) Å	T = 298 K
V = 1127.2 (2) Å^3	Block, violet
Z = 4	0.12 × 0.10 × 0.07 mm
F(000) = 1715.9

Data collection

Oxford Xcalibur 3 diffractometer	586 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.029
Graphite monochromator	θmax = 35.0°, θmin = 2.5°
ω scans	h = −16→16
Absorption correction: gaussian (ABSPACK; Oxford Diffraction, 2006)	k = −16→16
Tmin = 0.006, Tmax = 0.041	l = −18→18
2692 measured reflections	10 standard reflections every 150 reflections
673 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.011	w = 1/[σ^2(Fo^2) + (0.P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.011	(Δ/σ)max = 0.007
S = 0.88	Δρmax = 0.76 at 0.0000 0.0000 0.1996 (1.66 Å from TL) e Å^−3
673 reflections	Δρmin = −0.99 at 0.0000 0.0000 0.2500 (1.09 Å from TL) e Å^−3
37 parameters	Absolute structure: Flack (1983), No. of Friedel pairs?
0 restraints	Absolute structure parameter: 0.223 (14)

Special details

Experimental. The chemical composition was then determined using wavelength dispersive analysis (WDS) by means of a Jeol JXA-8600 electron microprobe. Major and minor elements were determined at a 20 kV accelerating voltage and a 40 nA beam current, with a counting time of 10 s. For the WDS analyses the following lines were used: S Kα, Fe Kα, Cu Kα, Zn Kα, As Lα, Ag Lα, Sb Lβ, Hg Lα, Tl Mα. The standards employed were pure metals for Cu, Ag, and Tl; pyrite for Fe and S; cinnabar for Hg; synthetic Sb₂S₃ for Sb; synthetic As₂S₃ for As; and synthetic ZnS for Zn.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Tl	0.0000	0.0000	0.34659 (2)	0.04983 (7)
Cu	0.0000	0.5000	0.2500	0.04981 (19)	0.644 (8)
Ag	0.0000	0.5000	0.2500	0.04981 (19)	0.356 (8)
Hg	0.21531 (2)	0.5000	0.5000	0.04991 (6)	0.851 (2)
Zn	0.21531 (2)	0.5000	0.5000	0.04991 (6)	0.149 (2)
As	0.26274 (5)	0.26274 (5)	0.24989 (13)	0.0499 (2)	0.848 (7)
Sb	0.26274 (5)	0.26274 (5)	0.24989 (13)	0.0499 (2)	0.152 (7)
S1	0.09444 (9)	0.33056 (7)	0.38015 (13)	0.04969 (18)
S2	0.12451 (7)	0.12451 (7)	0.1359 (2)	0.0505 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Tl	0.05002 (7)	0.05002 (7)	0.04945 (12)	−0.0003 (4)	0.000	0.000
Cu	0.0503 (2)	0.0503 (2)	0.0489 (3)	0.000	0.000	0.000
Ag	0.0503 (2)	0.0503 (2)	0.0489 (3)	0.000	0.000	0.000
Hg	0.04998 (10)	0.05017 (9)	0.04957 (10)	0.000	0.000	−0.0003 (3)
Zn	0.04998 (10)	0.05017 (9)	0.04957 (10)	0.000	0.000	−0.0003 (3)
As	0.0504 (3)	0.0504 (3)	0.0490 (2)	0.0004 (3)	0.0007 (6)	0.0007 (6)
Sb	0.0504 (3)	0.0504 (3)	0.0490 (2)	0.0004 (3)	0.0007 (6)	0.0007 (6)
S1	0.0499 (3)	0.0500 (3)	0.0491 (5)	−0.0005 (2)	0.0013 (5)	−0.0002 (5)
S2	0.0499 (3)	0.0499 (3)	0.0515 (9)	−0.0002 (3)	−0.0005 (4)	−0.0005 (4)

Geometric parameters (Å, º)

Tl—S1	3.4526 (8)	Hg—S1^viii	2.4808 (11)
Tl—S2^i	2.961 (2)	Hg—S2^ix	2.5428 (15)
Tl—S2	2.961 (2)	Hg—S2^x	2.5428 (15)
Tl—Tl^ii	3.4707 (6)	As—S1	2.3350 (14)
Tl—Sb^iii	3.5226 (9)	As—S1^xi	2.3350 (14)
Tl—Sb^iv	3.5226 (9)	As—S2	2.3387 (19)
Cu—S1^v	2.4325 (11)	S2—Zn^xii	2.5428 (15)
Cu—S1^vi	2.4325 (11)	S2—Zn^xiii	2.5428 (15)
Cu—S1	2.4325 (11)	S2—Hg^xiii	2.5428 (15)
Cu—S1^vii	2.4325 (11)	S2—Hg^xii	2.5428 (15)
Hg—S1	2.4808 (11)
S2^i—Tl—S2	72.83 (6)	S2^ix—Hg—S2^x	102.08 (6)
S2^i—Tl—Tl^ii	143.59 (3)	S1—As—S1^xi	91.08 (6)
S2—Tl—Tl^ii	143.59 (3)	S1—As—S2	95.41 (5)
S2^i—Tl—Sb^iii	75.56 (2)	S1^xi—As—S2	95.41 (5)
S2—Tl—Sb^iii	75.56 (2)	As—S1—Cu	95.65 (5)
Tl^ii—Tl—Sb^iii	108.05 (2)	As—S1—Hg	101.10 (4)
S2^i—Tl—Sb^iv	75.56 (2)	Cu—S1—Hg	92.59 (3)
S2—Tl—Sb^iv	75.56 (2)	As—S2—Zn^xii	104.52 (3)
Tl^ii—Tl—Sb^iv	108.05 (2)	As—S2—Zn^xiii	104.52 (3)
Sb^iii—Tl—Sb^iv	143.90 (5)	Zn^xii—S2—Zn^xiii	104.42 (8)
S1^v—Cu—S1^vi	105.50 (6)	As—S2—Hg^xiii	104.52 (3)
S1^v—Cu—S1	111.49 (3)	Zn^xii—S2—Hg^xiii	104.42 (8)
S1^vi—Cu—S1	111.49 (3)	As—S2—Hg^xii	104.52 (3)
S1^v—Cu—S1^vii	111.49 (3)	Zn^xiii—S2—Hg^xii	104.42 (8)
S1^vi—Cu—S1^vii	111.49 (3)	Hg^xiii—S2—Hg^xii	104.42 (8)
S1—Cu—S1^vii	105.50 (6)	As—S2—Tl	92.97 (9)
S1—Hg—S1^viii	121.80 (4)	Zn^xii—S2—Tl	123.05 (3)
S1—Hg—S2^ix	107.97 (5)	Zn^xiii—S2—Tl	123.05 (3)
S1^viii—Hg—S2^ix	107.64 (4)	Hg^xiii—S2—Tl	123.05 (3)
S1—Hg—S2^x	107.64 (4)	Hg^xii—S2—Tl	123.05 (3)
S1^viii—Hg—S2^x	107.97 (5)

Symmetry codes: (i) −x, −y, z; (ii) x, −y, −z+1; (iii) x−1/2, −y+1/2, −z+1/2; (iv) −x+1/2, y−1/2, −z+1/2; (v) y−1/2, −x+1/2, −z+1/2; (vi) −y+1/2, x+1/2, −z+1/2; (vii) −x, −y+1, z; (viii) x, −y+1, −z+1; (ix) −x+1/2, y+1/2, −z+1/2; (x) −x+1/2, −y+1/2, z+1/2; (xi) y, x, z; (xii) −y+1/2, −x+1/2, z−1/2; (xiii) −x+1/2, −y+1/2, z−1/2.