inorganic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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ISSN: 2056-9890

Schaurteite, Ca3Ge(SO4)2(OH)6·3H2O

aDepartment of Geosciences, University of Arizona, Tucson, AZ 85721, USA
*Correspondence e-mail: moriglie@email.arizona.edu

(Received 27 November 2012; accepted 14 December 2012; online 12 January 2013)

This report presents the first crystal structure determination of the mineral schaurteite, ideally Ca3Ge(SO4)2(OH)6·3H2O, tricalcium germanium bis­(sulfate) hexa­hydroxide trihydrate. This single-crystal X-ray diffraction study investigated a natural sample from the type locality at Tsumeb, Namibia. Schaurteite is a member of the fleischerite group of minerals, which also includes fleischerite, despujolsite, and mallestigite. The structure of schaurteite consists of slabs of Ca(O,OH,H2O)8 polyhedra (site symmetry mm2) inter­leaved with a mixed layer of Ge(OH)6 octa­hedra (-3m.) and SO4 tetra­hedra (3m.). There are two H atoms in the asymmetric unit, both located by full-matrix refinement, and both forming O—H⋯O hydrogen bonds.

Related literature

For the original description of schaurteite, see: Strunz & Tennyson (1967[Strunz, H. & Tennyson, C. (1967). Festschrift Dr. Werner T. Schaurte, pp. 33-47. Neuss-Rhein, Germany: Bauer & Schaurte.]). For descriptions of related minerals: fleischerite (Frondel & Strunz, 1960[Frondel, C. & Strunz, H. (1960). Neues Jahrb. Mineral. Monatsh. 1960, 132-142.]); despujolsite (Gaudefroy et al., 1968[Gaudefroy, C., Granger, M. M., Permingeat, F. & Protas, J. (1968). Bull. Soc. Fr. Minéral. Cristallogr. 91, 43-50.]); mallestigite (Sima et al., 1996[Sima, I., Ettinger, K., Koppelhuber-Bitschnau, B., Taucher, J. & Walter, F. (1996). Mitteilungen der Österreichischen Mineralogischen Gesellschaft, 141, 224-225.]). For structural refinements of related minerals: despujolsite (Barkley et al., 2011[Barkley, M. C., Yang, H., Evans, S. H., Downs, R. T. & Origlieri, M. J. (2011). Acta Cryst. E67, i47-i48.]); fleischerite (Otto, 1975[Otto, H. H. (1975). Neues Jahrb. Mineral. Abh. 123, 160-190.]). For analysis of anisotropic displacement parameters, see: Downs (2000[Downs, R. T. (2000). Rev. Mineral. Geochem. 41, 61-88.]).

Experimental

Crystal data
  • Ca3Ge(SO4)2(OH)6(H2O)3

  • Mr = 541.05

  • Hexagonal, P 63 /m m c

  • a = 8.5253 (4) Å

  • c = 10.8039 (6) Å

  • V = 680.03 (6) Å3

  • Z = 2

  • Mo Kα radiation

  • μ = 3.79 mm−1

  • T = 296 K

  • 0.05 × 0.03 × 0.03 mm

Data collection
  • Bruker APEXII CCD diffractometer

  • Absorption correction: multi-scan (SADABS; Sheldrick, 2005[Sheldrick, G. M. (2005). SADABS. University of Göttingen, Germany.]) Tmin = 0.656, Tmax = 0.747

  • 17243 measured reflections

  • 536 independent reflections

  • 456 reflections with I > 2σ(I)

  • Rint = 0.061

Refinement
  • R[F2 > 2σ(F2)] = 0.022

  • wR(F2) = 0.045

  • S = 1.15

  • 536 reflections

  • 35 parameters

  • All H-atom parameters refined

  • Δρmax = 0.40 e Å−3

  • Δρmin = −0.42 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
O3—H1⋯O2i 0.73 (3) 2.12 (3) 2.823 (2) 164 (3)
O4—H2⋯O1ii 0.79 (3) 2.04 (3) 2.789 (2) 158 (3)
Symmetry codes: (i) y, x, -z; (ii) [y, -x+y, z+{\script{1\over 2}}].

Data collection: APEX2 (Bruker, 2004[Bruker (2004). APEX2. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2005[Bruker (2005). SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: XtalDraw (Downs & Hall-Wallace, 2003[Downs, R. T. & Hall-Wallace, M. (2003). Am. Mineral. 88, 247-250.]); software used to prepare material for publication: SHELXL97.

Supporting information


Comment top

Schaurteite, Ca3Ge(SO4)2(OH)6.3H2O, is a rare germanium mineral found in oxidized germanite ores at the Tsumeb Corporation mine, Tsumeb, Namibia (Strunz & Tennyson, 1967). Schaurteite belongs to the fleischerite group of isotypic minerals, along with mallestigite, Pb3Sb(SO4)(AsO4)(OH)6.3H2O (Sima et al. 1996), despujolsite, Ca3Mn4+(SO4)2(OH)6.3H2O (Gaudefroy et al. 1968), and fleischerite, Pb3Ge(SO4)2(OH)6.3H2O (Frondel & Strunz, 1960). Of these four minerals, only despujolsite (Barkley et al. 2011) and synthetic fleischerite (Otto, 1975) have reported structures. This study represents the first structural report for schaurteite.

The crystal structure of schaurteite consists of slabs of Ca(OH)4O2(H2O)2 polyhedra (mm. symmetry), interconnected by mixed layers of Ge(OH)6 octahedra (3m. symmetry) and SO4 tetrahedra (3m. symmetry) (Figures 1,2). The mean Ca—O, Ge—O, and S—O bond lengths are 2.487 Å, 1.895 Å, and 1.468 Å, respectively. There are two separate hydrogen atoms, H1 bonded to the O3 atom coordinating Ge, and H2 bonded to the O4 atom (mm. symmetry) which generates an H2O molecule. Both H atoms form hydrogen bonds, O3—H1···O2 and O4—H2···O1 (Figure 3), mimicking those seen in despujolsite (Barkley et al. 2011).

In the original description of schaurteite, Strunz and Tennyson (1967) noted systematic absences in X-ray photographs consistent with three different space groups: P63/mmc, P63mc, and P62c. Supposing an isostructural relationship with despujolsite (Barkley et al. 2011), this study initially refined schaurteite in space group P62c with a favorable Robs of 0.0251 for 45 parameters. Despite the relatively low R factor, the positional parameters for H2 did not converge, and a twin model showed a racemic component of 47%, indicating centrosymmetry in the structure. In space group P63/mmc, the structural refinement converged rapidly for all atomic coordinates including those for H, and Robs dropped to .0219 for 35 parameters. Consequently, this study proposes P63/mmc symmetry for schaurteite, in contrast to P62c symmetry reported for both fleischerite (Otto, 1975) and despujolsite (Barkley et al. 2011). Curiously, schaurteite, Ca3Ge(SO4)2(OH)6.3H2O, and fleischerite, Pb3Ge(SO4)2(OH)6.3H2O, are both single locality mineral species occurring at the same deposit, notably lacking significant solid solution between Pb and Ca in their reported analyses (Strunz and Tennyson, 1967; this study; Frondel and Strunz, 1960). If unbonded lone pair electrons belonging to Pb in fleischerite disrupt the centrosymmetry seen in schaurteite, this would explain an ostensibly limited solid solution between fleischerite and schaurteite.

Previous studies of fleischerite group minerals noted relatively large displacement parameters for O atoms in the SO4 tetrahedron. For this reason, Otto (1975) proposed a split site for the O1 atom in the structure of synthetic fleischerite. When Barkley et al. (2011) reported the structure of the isotypic Mn4+ analog despujolsite, they also noted large displacement parameters for O1. However, Barkley et al. (2011) proposed a single O1 site for despujolsite after an analysis of the displacement parameters demonstrated that the SO4 group behaves as a rigid body with significant translation (0.72 Å) and libration (7.95°). Using translation-libration-screw motion (TLS) modelling software (Downs, 2000), the SO4 group in schaurteite similarly shows rigid body behavior with 0.73 Å of translation and 7.97° of libration. Consequently, this study proposes a single O1 atom model for schaurteite (Figure 4).

Related literature top

For the original description of schaurteite, see: Strunz & Tennyson (1967). For descriptions of related minerals: fleischerite (Frondel & Strunz, 1960); despujolsite (Gaudefroy et al., 1968); mallestigite (Sima et al. 1996). For structural refinements of related minerals: despujolsite (Barkley et al., 2011); fleischerite (Otto, 1975). For analysis of anisotropic displacement parameters, see: Downs (2000).

Experimental top

The schaurteite specimen used in this study came from the Tsumeb Corporation mine, Tsumeb, Otavi Mountains, Namibia and remains on deposition (sample R120104) with the RRUFF project (http://www.rruff.info). Schaurteite forms colorless fibrous crystals in a matrix of quartz, calcite, and germanite.

Chemical analyses were performed on a Cameca SX-100 electron microprobe at the Lunar and Planetary Laboratory, University of Arizona. The electron microprobe sample and the single-crystal fragment came from the same parent sample. Like despujolsite (Barkley et al. 2011), schaurteite was fugitive under the electron beam, leading to the choice of the following operating conditions: 20 kV exciting voltage, 6 nA operating current, and a spot size of 5 microns. The average of 13 analyses gave GeO2 17.97%, CaO 30.41%, and SO3 29.22%. Normalizing to 17 O atoms (which includes 6 moles H2O per formula unit), the combined empirical and structural chemical formula becomes Ca3.01Ge0.95(S2.03O8)(OH)6.3H2O. Further details of the electron microprobe analysis and formula calculations are available on the RRUFF web site (http://www.rruff.info/R120104).

Refinement top

To model possible variable occupancy of cations, site occupancies were allowed to vary without restraints. The results justified a model with full occupancies of Ca, Ge, and S, corroborated by electron microprobe data showing only these elements (with Z > 8). Two hydrogen atom positions were refined without restraints, both with reasonable isotropic displacement parameters.

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); 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 top
[Figure 1] Fig. 1. Polyhedral view of the schaurteite structure down [100], with slabs of light blue Ca(OH)4O2(H2O)2 polyhedra, interleaved with a mixed layer of green Ge(OH)6 octahedra and yellow SO4 tetrahedra. Unit cell outline shown in black.
[Figure 2] Fig. 2. Polyhedral view of the schaurteite structure down [001], showing a single layer of light blue Ca(OH)4O2(H2O)2 polyhedra, a single mixed layer of green Ge(OH)6 octahedra and yellow SO4 tetrahedra, and dark blue H atoms in both layers.
[Figure 3] Fig. 3. Hydrogen bonding in schaurteite, showing O4—H2···O1 at 2.04 Å and O3—H1···O2 at 2.12 Å.
[Figure 4] Fig. 4. Ellipsoidal view of the schaurteite structure down [001], showing red O atoms, yellow S atoms, green Ge atoms, and light blue Ca atoms. Unit cell outline shown in black. The large circular ellipsoid at [2/3,1/3,z] represents the O1 atom (3 m. symmetry), which forms the apex of a rigid SO4 tetrahedron with significant translation (0.73 Å) and libration (7.97°).
Tricalcium germanium bis(sulfate) hexahydroxide trihydrate top
Crystal data top
Ca3Ge(SO4)2(OH)6(H2O)3Dx = 2.642 Mg m3
Mr = 541.05Mo Kα radiation, λ = 0.71073 Å
Hexagonal, P63/mmcCell parameters from 2603 reflections
Hall symbol: -P 6c 2cθ = 2.8–28.0°
a = 8.5253 (4) ŵ = 3.79 mm1
c = 10.8039 (6) ÅT = 296 K
V = 680.03 (6) Å3Hexagonal prism section, colourless
Z = 20.05 × 0.03 × 0.03 mm
F(000) = 544
Data collection top
Bruker APEXII CCD
diffractometer
536 independent reflections
Radiation source: fine-focus sealed tube456 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.061
ϕ and ω scansθmax = 33.1°, θmin = 2.8°
Absorption correction: multi-scan
(SADABS; Sheldrick, 2005)
h = 1013
Tmin = 0.656, Tmax = 0.747k = 1313
17243 measured reflectionsl = 1616
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.022Hydrogen site location: difference Fourier map
wR(F2) = 0.045All H-atom parameters refined
S = 1.15 w = 1/[σ2(Fo2) + (0.0131P)2 + 0.5886P]
where P = (Fo2 + 2Fc2)/3
536 reflections(Δ/σ)max < 0.001
35 parametersΔρmax = 0.40 e Å3
0 restraintsΔρmin = 0.42 e Å3
Crystal data top
Ca3Ge(SO4)2(OH)6(H2O)3Z = 2
Mr = 541.05Mo Kα radiation
Hexagonal, P63/mmcµ = 3.79 mm1
a = 8.5253 (4) ÅT = 296 K
c = 10.8039 (6) Å0.05 × 0.03 × 0.03 mm
V = 680.03 (6) Å3
Data collection top
Bruker APEXII CCD
diffractometer
536 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2005)
456 reflections with I > 2σ(I)
Tmin = 0.656, Tmax = 0.747Rint = 0.061
17243 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0220 restraints
wR(F2) = 0.045All H-atom parameters refined
S = 1.15Δρmax = 0.40 e Å3
536 reflectionsΔρmin = 0.42 e Å3
35 parameters
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 (Å2) top
xyzUiso*/Ueq
Ge0.00000.00000.00000.00762 (11)
Ca0.30387 (8)0.15193 (4)0.25000.01107 (12)
S0.33330.66670.52599 (7)0.00963 (16)
O10.33330.66670.1106 (2)0.0167 (5)
O20.4786 (2)0.23930 (11)0.06925 (14)0.0190 (3)
O30.10006 (10)0.2001 (2)0.10982 (13)0.0106 (3)
O40.50772 (16)0.49228 (16)0.75000.0190 (5)
H10.142 (2)0.284 (4)0.075 (2)0.028 (8)*
H20.543 (2)0.457 (2)0.695 (3)0.051 (11)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ge0.00878 (15)0.00878 (15)0.0053 (2)0.00439 (7)0.0000.000
Ca0.0098 (3)0.0131 (2)0.0091 (2)0.00491 (13)0.0000.000
S0.0108 (2)0.0108 (2)0.0073 (3)0.00538 (11)0.0000.000
O10.0217 (9)0.0217 (9)0.0067 (11)0.0109 (4)0.0000.000
O20.0114 (7)0.0243 (7)0.0169 (7)0.0057 (4)0.0039 (6)0.0020 (3)
O30.0131 (5)0.0086 (7)0.0087 (6)0.0043 (3)0.0004 (3)0.0008 (5)
O40.0239 (9)0.0239 (9)0.0143 (10)0.0158 (10)0.0000.000
Geometric parameters (Å, º) top
Ge—O31.8949 (14)Ca—O3iii2.4890 (9)
Ge—O3i1.8949 (14)Ca—O3vii2.4890 (9)
Ge—O3ii1.8949 (14)Ca—O4viii2.6284 (12)
Ge—O3iii1.8949 (14)Ca—O4ix2.6284 (12)
Ge—O3iv1.8949 (14)S—O2x1.4651 (16)
Ge—O3v1.8949 (14)S—O2xi1.4651 (16)
Ca—O22.3404 (15)S—O2xii1.4651 (16)
Ca—O2vi2.3404 (15)S—O1vi1.475 (3)
Ca—O32.4890 (9)O3—H10.73 (3)
Ca—O3vi2.4890 (9)O4—H20.79 (3)
O3—Ge—O3i180.0O2—Ca—O3vii147.24 (3)
O3—Ge—O3ii95.05 (6)O2vi—Ca—O3vii79.95 (4)
O3i—Ge—O3ii84.95 (6)O3—Ca—O3vii105.61 (6)
O3—Ge—O3iii84.95 (6)O3vi—Ca—O3vii61.87 (7)
O3i—Ge—O3iii95.05 (6)O3iii—Ca—O3vii74.96 (5)
O3ii—Ge—O3iii180.00 (10)O2—Ca—O4viii73.04 (3)
O3—Ge—O3iv95.05 (6)O2vi—Ca—O4viii73.04 (3)
O3i—Ge—O3iv84.95 (6)O3—Ca—O4viii83.33 (5)
O3ii—Ge—O3iv84.95 (6)O3vi—Ca—O4viii83.33 (5)
O3iii—Ge—O3iv95.05 (6)O3iii—Ca—O4viii139.12 (3)
O3—Ge—O3v84.95 (6)O3vii—Ca—O4viii139.12 (3)
O3i—Ge—O3v95.05 (6)O2—Ca—O4ix73.04 (3)
O3ii—Ge—O3v95.05 (6)O2vi—Ca—O4ix73.04 (3)
O3iii—Ge—O3v84.95 (6)O3—Ca—O4ix139.12 (3)
O3iv—Ge—O3v180.00 (14)O3vi—Ca—O4ix139.12 (3)
O2—Ca—O2vi113.10 (8)O3iii—Ca—O4ix83.33 (5)
O2—Ca—O379.95 (4)O3vii—Ca—O4ix83.33 (5)
O2vi—Ca—O3147.24 (3)O4viii—Ca—O4ix116.09 (10)
O2—Ca—O3vi147.24 (3)O2—Ca—Ge73.16 (4)
O2vi—Ca—O3vi79.95 (4)O2x—S—O2xi110.32 (7)
O3—Ca—O3vi74.96 (5)O2x—S—O2xii110.32 (7)
O2—Ca—O3iii79.95 (4)O2xi—S—O2xii110.32 (7)
O2vi—Ca—O3iii147.24 (3)O2x—S—O1vi108.61 (7)
O3—Ca—O3iii61.87 (7)O2xi—S—O1vi108.60 (7)
O3vi—Ca—O3iii105.61 (6)O2xii—S—O1vi108.60 (7)
Symmetry codes: (i) x, y, z; (ii) xy, x, z; (iii) x+y, x, z; (iv) y, x+y, z; (v) y, xy, z; (vi) x, y, z+1/2; (vii) x+y, x, z+1/2; (viii) x+1, y+1, z+1; (ix) y, x+y, z+1; (x) y, x+y+1, z+1/2; (xi) x+1, y+1, z+1/2; (xii) xy, x, z+1/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H1···O2xiii0.73 (3)2.12 (3)2.823 (2)164 (3)
O4—H2···O1xiv0.79 (3)2.04 (3)2.789 (2)158 (3)
Symmetry codes: (xiii) y, x, z; (xiv) y, x+y, z+1/2.

Experimental details

Crystal data
Chemical formulaCa3Ge(SO4)2(OH)6(H2O)3
Mr541.05
Crystal system, space groupHexagonal, P63/mmc
Temperature (K)296
a, c (Å)8.5253 (4), 10.8039 (6)
V3)680.03 (6)
Z2
Radiation typeMo Kα
µ (mm1)3.79
Crystal size (mm)0.05 × 0.03 × 0.03
Data collection
DiffractometerBruker APEXII CCD
diffractometer
Absorption correctionMulti-scan
(SADABS; Sheldrick, 2005)
Tmin, Tmax0.656, 0.747
No. of measured, independent and
observed [I > 2σ(I)] reflections
17243, 536, 456
Rint0.061
(sin θ/λ)max1)0.769
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.022, 0.045, 1.15
No. of reflections536
No. of parameters35
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.40, 0.42

Computer programs: APEX2 (Bruker, 2004), SAINT (Bruker, 2005), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), XtalDraw (Downs & Hall-Wallace, 2003).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H1···O2i0.73 (3)2.12 (3)2.823 (2)164 (3)
O4—H2···O1ii0.79 (3)2.04 (3)2.789 (2)158 (3)
Symmetry codes: (i) y, x, z; (ii) y, x+y, z+1/2.
 

Acknowledgements

The authors thank the Arizona Science Foundation for their support. Thanks to Stephen G. West for systems support. This paper benefited greatly from the comments of Sean Parkin, who recognized the likehood of centrosymmetry in schaurteite.

References

First citationBarkley, M. C., Yang, H., Evans, S. H., Downs, R. T. & Origlieri, M. J. (2011). Acta Cryst. E67, i47–i48.  Web of Science CrossRef IUCr Journals
First citationBruker (2004). APEX2. Bruker AXS Inc., Madison, Wisconsin, USA.
First citationBruker (2005). SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.
First citationDowns, R. T. (2000). Rev. Mineral. Geochem. 41, 61–88.  CrossRef
First citationDowns, R. T. & Hall-Wallace, M. (2003). Am. Mineral. 88, 247–250.  CAS
First citationFrondel, C. & Strunz, H. (1960). Neues Jahrb. Mineral. Monatsh. 1960, 132–142.
First citationGaudefroy, C., Granger, M. M., Permingeat, F. & Protas, J. (1968). Bull. Soc. Fr. Minéral. Cristallogr. 91, 43–50.  CAS
First citationOtto, H. H. (1975). Neues Jahrb. Mineral. Abh. 123, 160–190.
First citationSheldrick, G. M. (2005). SADABS. University of Göttingen, Germany.
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals
First citationSima, I., Ettinger, K., Koppelhuber-Bitschnau, B., Taucher, J. & Walter, F. (1996). Mitteilungen der Österreichischen Mineralogischen Gesellschaft, 141, 224–225.
First citationStrunz, H. & Tennyson, C. (1967). Festschrift Dr. Werner T. Schaurte, pp. 33–47. Neuss-Rhein, Germany: Bauer & Schaurte.

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