Redetermination of conichalcite, CaCu(AsO4)(OH)

Henderson, R.R.; Yang, H.; Downs, R.T.; Jenkins, R.A.

doi:10.1107/S1600536808024173

inorganic compounds

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Volume 64| Part 9| September 2008| Pages i53-i54

doi:10.1107/S1600536808024173

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Redetermination of conichalcite, CaCu(AsO₄)(OH)

Rachel R. Henderson,^a Hexiong Yang,^a ^* Robert T. Downs ^a and Robert A. Jenkins ^a

^aDepartment of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, AZ 85721-0077, USA
^*Correspondence e-mail: hyang@u.arizona.edu

(Received 2 July 2008; accepted 29 July 2008; online 6 August 2008)

The crystal structure of conichalcite [calcium copper(II) arsenate(V) hydroxide], with ideal formula CaCu(AsO₄)(OH), was redetermined from a natural twinned specimen found in the Maria Catalina mine (Chile). In contrast to the previous refinement from photographic data [Qurashi & Barnes (1963 ). Can. Mineral. 7, 561–577], all atoms were refined with anisotropic displacement parameters and with the H atom located. Conichalcite belongs to the adelite mineral group. The Jahn–Teller-distorted [CuO₆] octahedra share edges, forming chains running parallel to [010]. These chains are cross-linked by eight-coordinate Ca atoms and by sharing vertices with isolated AsO₄ tetrahedra. Of five calcium arsenate minerals in the adelite group, the [MO₆] (M = Cu, Zn, Co, Ni and Mg) octahedron in conichalcite is the most distorted, and the donor–acceptor O—H⋯O distance is the shortest.

Related literature

For background on the adelite mineral family, see: Qurashi & Barnes (1963, 1964 ); Qurashi et al. (1953 ). For structure refinements in the adelite group, see: Effenberger et al. (2002 ) for adelite, CaMgAsO₄(OH); Clark et al. (1997 ) and Giuseppetti & Tadini (1988 ) for austinite, CaZnAsO₄(OH); Yang et al. (2007 ) for cobaltaustinite, CaCoAsO₄(OH); Cesbron et al. (1987 ) for nickelaustinite, CaNiAsO₄(OH). Correlations between O—H streching frequencies and O—H⋯O donor–acceptor distances are given by Libowitzky (1999 ). Raman spectroscopic data on some minerals of the adelite group have been reported by Martens et al. (2003 ); for general background, see: Robinson et al. (1971 ).

Experimental

Crystal data

CaCu(AsO₄)(OH)
M_r = 259.57
Orthorhombic, P 2₁ 2₁ 2₁
a = 7.3822 (2) Å
b = 5.8146 (2) Å
c = 9.2136 (3) Å
V = 395.49 (2) Å³
Z = 4
Mo Kα radiation
μ = 15.03 mm⁻¹
T = 293 (2) K
0.06 × 0.05 × 0.04 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (TWINABS; Sheldrick, 2008 ) T_min = 0.492, T_max = 0.585 (expected range = 0.461–0.548)
7088 measured reflections
1602 independent reflections
1487 reflections with I > 2σ(I)
R_int = 0.023

Refinement

R[F² > 2σ(F²)] = 0.018
wR(F²) = 0.038
S = 1.03
1602 reflections
79 parameters
All H-atom parameters refined
Δρ_max = 0.63 e Å⁻³
Δρ_min = −0.49 e Å⁻³
Absolute structure: Flack (1983 ), 644 Friedel pairs
Flack parameter: 0.00 (2)

Table 1
Selected bond lengths (Å)

Ca—O5ⁱ	2.3626 (13)
Ca—O3ⁱⁱ	2.3995 (17)
Ca—O4ⁱⁱⁱ	2.4818 (16)
Ca—O2^iv	2.5178 (17)
Ca—O4^v	2.5281 (16)
Ca—O1^iv	2.5462 (14)
Ca—O3	2.5786 (17)
Ca—O2	2.6264 (17)
Cu—O5	1.8850 (15)
Cu—O5^vi	1.8855 (16)
Cu—O1^vi	2.0666 (16)
Cu—O1	2.0688 (15)
Cu—O3^vii	2.2976 (15)
Cu—O4^viii	2.3882 (14)
As—O4	1.6749 (16)
As—O3	1.6779 (16)
As—O2	1.6796 (16)
As—O1	1.7099 (13)
Symmetry codes: (i) $[-x+{\script{1\over 2}}, -y+1, z-{\script{1\over 2}}]$ ; (ii) $[x+{\script{1\over 2}}, -y+{\script{3\over 2}}, -z]$ ; (iii) x, y+1, z; (iv) $[-x+1, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (v) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z]$ ; (vi) $[-x, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (vii) $[x-{\script{1\over 2}}, -y+{\script{1\over 2}}, -z]$ ; (viii) $[-x+{\script{1\over 2}}, -y, z+{\script{1\over 2}}]$ .

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O5—H1⋯O2^ix	0.86 (4)	1.91 (4)	2.678 (2)	149 (3)
Symmetry code: (ix) x-1, y, z.

Data collection: APEX2 (Bruker, 2003 ); cell refinement: SAINT (Bruker, 2005 ); data reduction: SAINT; 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: SHELXTL (Sheldrick, 2008).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808024173/wm2185sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536808024173/wm2185Isup2.hkl

checkCIF report

Comment top

Minerals of the adelite group crystallize with orthorhombic symmetry in space group P2₁2₁2₁ (Qurashi & Barnes, 1963, 1964) and have a general chemical formula A^+,2+M^2+,3+(X^4+,5+,6+O₄)(OH), where A = Na, Ca, Pb, M = Al, Mg, Zn, Mn, Fe, Co, Cu, Ni, and X = Si, P, V, As. There are five calcium arsenates in this group: adelite CaMgAsO₄(OH), austinite CaZnAsO₄(OH), conichalcite CaCuAsO₄(OH), nickelaustinite CaNiAsO₄(OH), and cobaltaustinite, CaCoAsO₄(OH). All structures of these calcium arsenate minerals have been determined previously (Qurashi & Barnes, 1963; Cesbron et al., 1987; Giuseppetti & Tadini, 1988; Clark et al., 1997; Effenberger et al., 2002; Yang et al., 2007). However, in our efforts to understand the relationships between the hydrogen bonding schemes and Raman spectra of hydrous minerals, we noted that the structural information of conichalcite needs to be improved, because this structure was refined by Qurashi & Barnes (1963) with X-ray intensity data collected by Qurashi et al. (1953) from precession photographs without anisotropic displacement parameters and localisation of the H atom position.

Conichalcite can be compared with the other Ca-arsenate minerals in the adelite group. The distorted [CuO₆] octahedra (i.e. elongated tetragonal bipyramids) share edges to form chains running parallel to [010], which are cross-linked by Ca atoms and by sharing vertices with isolated AsO₄ tetrahedra (Fig. 1). The principal difference among the five calcium arsenates in the group is manifested in the bonding environments around the octahedrally coordinated M cations. The average M—O bond lengths appear to decrease from <Zn—O> (= 2.106 Å) in austinite (Clark et al., 1997), to <Cu—O> (= 2.099 Å) in conichalcite, <Co—O> (= 2.092 Å) in cobaltaustinite (Yang et al., 2007), <Ni—O> (= 2.085 Å) in nickelaustinite (Cesbron et al., 1987), and to <Mg—O> (= 2.075 Å) in adelite (Effenberger et al., 2002). Of these [MO₆] octahedra, the Cu-octahedron, due to its strong Jahn-Teller effect, displays the greatest distortion in terms of the tetragonal elongation and angle variance (Robinson et al., 1971), which are 1.0229 and 23.58, respectively.

The donor-acceptor O5—H···O2 distance in conichalcite is 2.678 (2) Å, which is the shortest of all five Ca-arsenates in the adelite group [2.723 (2) Å in austinite (Clark et al., 1997), 2.721 (7) Å in cobaltaustinite (Yang et al., 2007), 2.73 (1) Å in nickelaustinite (Cesbron et al., 1987), and 2.766 (2) Å in adelite (Effenberger et al., 2002)]. As the O—H stretching frequencies (ν_OH) increase with the O—H···O distance (Libowitzky,1999), we should expect the smallest ν_OH value for conichalcite and the largest for adelite among the five calcium arsenates in the adelite group. Indeed, the major ν_OH band positions determined from Raman spectra for conichalcite and adelite are, respectively, 3158 and 3550 cm^-1 from Martens et al. (2003), or 3161 and 3423 cm^-1 from the RRUFF project (http://rruff.info), with intermediate ν_OH values for the other three minerals (austinite, cobaltaustinite, and nickelaustinite).

Related literature top

For background on the adelite mineral family, see: Qurashi & Barnes (1963, 1964); Qurashi et al. (1953). For structure refinements in the adelite group, see: Effenberger et al. (2002) for adelite, CaMgAsO₄(OH); Clark et al. (1997) and Giuseppetti & Tadini (1988) for austinite, CaZnAsO₄(OH); Yang et al. (2007) for cobaltaustinite, CaCoAsO₄(OH); Cesbron et al. (1987) for nickelaustinite, CaNiAsO₄(OH). Correlations between O—H streching frequencies and O—H···O donor–acceptor distances are given by Libowitzky (1999). Raman spectroscopic data on some minerals of the adelite group have been reported by Martens et al. (2003); for general background, see: Robinson et al. (1971).

Experimental top

The conichalcite crystal used in this study is from Maria Catalina mine, Pampa Larga Mining District, Tierra Amarilla, Chile, and is a sample from the RRUFF project (deposition No. R070430; http//rruff.info). The chemical composition, Ca(Cu_0.99Zn_0.01)(AsO₄)(OH), was determined with a CAMECA SX50 electron microprobe (http//rruff.info).

Computing details top

Data collection: APEX2 (Bruker, 2003); 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: SHELXTL (Sheldrick, 2008).

Figures top

Fig. 1. The crystal structure of conichalcite. Green octahedra, yellow tetrahedra, grey large sphares, and red small spheres represent [CuO₆], [AsO₄], Ca, and H, respectively. Hydrogen bonding is indicated with blue lines.

calcium copper(II) arsenate(V) hydroxide top

Crystal data top

CaCu(AsO₄)(OH)	F(000) = 492
M_r = 259.57	D_x = 4.359 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 3371 reflections
a = 7.3822 (2) Å	θ = 3.6–34.0°
b = 5.8146 (2) Å	µ = 15.03 mm⁻¹
c = 9.2136 (3) Å	T = 293 K
V = 395.49 (2) Å³	Euhedral, equant, green
Z = 4	0.06 × 0.05 × 0.04 mm

Data collection top

Bruker APEX2 CCD diffractometer	1602 independent reflections
Radiation source: fine-focus sealed tube	1487 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.023
ϕ and ω scans	θ_max = 34.0°, θ_min = 3.5°
Absorption correction: multi-scan (TWINABS; Sheldrick, 2008)	h = −9→11
T_min = 0.492, T_max = 0.585	k = −9→9
7088 measured reflections	l = −14→14

Refinement top

Refinement on F²	Hydrogen site location: difference Fourier map
Least-squares matrix: full	All H-atom parameters refined
R[F² > 2σ(F²)] = 0.018	w = 1/[σ²(F_o²) + (0.0151P)² + 0.1227P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.038	(Δ/σ)_max < 0.001
S = 1.03	Δρ_max = 0.63 e Å⁻³
1602 reflections	Δρ_min = −0.49 e Å⁻³
79 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0029 (5)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack (1983), 644 Friedel pairs
Secondary atom site location: difference Fourier map	Absolute structure parameter: 0.00 (2)

Crystal data top

CaCu(AsO₄)(OH)	V = 395.49 (2) Å³
M_r = 259.57	Z = 4
Orthorhombic, P2₁2₁2₁	Mo Kα radiation
a = 7.3822 (2) Å	µ = 15.03 mm⁻¹
b = 5.8146 (2) Å	T = 293 K
c = 9.2136 (3) Å	0.06 × 0.05 × 0.04 mm

Data collection top

Bruker APEX2 CCD diffractometer	1602 independent reflections
Absorption correction: multi-scan (TWINABS; Sheldrick, 2008)	1487 reflections with I > 2σ(I)
T_min = 0.492, T_max = 0.585	R_int = 0.023
7088 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.018	All H-atom parameters refined
wR(F²) = 0.038	Δρ_max = 0.63 e Å⁻³
S = 1.03	Δρ_min = −0.49 e Å⁻³
1602 reflections	Absolute structure: Flack (1983), 644 Friedel pairs
79 parameters	Absolute structure parameter: 0.00 (2)
0 restraints

Special details top

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 (Å²) top

	x	y	z	U_iso*/U_eq
Ca	0.61727 (5)	0.72961 (8)	0.07340 (4)	0.01133 (12)
Cu	−0.00416 (4)	−0.00002 (6)	0.25029 (4)	0.00898 (8)
As	0.36728 (2)	0.26438 (4)	0.08118 (2)	0.00768 (6)
O1	0.18844 (17)	0.2450 (3)	0.19847 (15)	0.0135 (3)
O2	0.5395 (2)	0.3313 (3)	0.19256 (18)	0.0187 (4)
O3	0.3514 (2)	0.4927 (3)	−0.02947 (17)	0.0157 (3)
O4	0.3885 (2)	0.0147 (3)	−0.00782 (15)	0.0145 (4)
O5	−0.13880 (18)	0.2539 (3)	0.31777 (14)	0.0113 (3)
H1	−0.229 (5)	0.232 (6)	0.260 (3)	0.055 (11)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ca	0.01169 (18)	0.0119 (2)	0.01041 (18)	−0.00064 (17)	−0.00072 (13)	0.00020 (18)
Cu	0.00885 (11)	0.00621 (12)	0.01190 (12)	0.00029 (9)	0.00211 (8)	−0.00121 (8)
As	0.00801 (8)	0.00659 (9)	0.00845 (9)	0.00006 (8)	0.00059 (7)	0.00014 (9)
O1	0.0141 (6)	0.0107 (7)	0.0157 (6)	−0.0025 (7)	0.0035 (5)	−0.0006 (7)
O2	0.0146 (7)	0.0212 (9)	0.0205 (8)	−0.0029 (6)	−0.0048 (6)	0.0004 (7)
O3	0.0201 (7)	0.0107 (7)	0.0164 (7)	0.0011 (7)	0.0044 (7)	0.0035 (6)
O4	0.0181 (8)	0.0096 (7)	0.0158 (8)	0.0018 (6)	0.0022 (7)	−0.0018 (6)
O5	0.0106 (5)	0.0102 (6)	0.0132 (6)	0.0000 (8)	0.0002 (5)	−0.0003 (6)

Geometric parameters (Å, º) top

Ca—O5ⁱ	2.3626 (13)	Cu—O5^vi	1.8855 (16)
Ca—O3ⁱⁱ	2.3995 (17)	Cu—O1^vi	2.0666 (16)
Ca—O4ⁱⁱⁱ	2.4818 (16)	Cu—O1	2.0688 (15)
Ca—O2^iv	2.5178 (17)	Cu—O3^vii	2.2976 (15)
Ca—O4^v	2.5281 (16)	Cu—O4^viii	2.3882 (14)
Ca—O1^iv	2.5462 (14)	As—O4	1.6749 (16)
Ca—O3	2.5786 (17)	As—O3	1.6779 (16)
Ca—O2	2.6264 (17)	As—O2	1.6796 (16)
Cu—O5	1.8850 (15)	As—O1	1.7099 (13)

O5ⁱ—Ca—O3ⁱⁱ	75.88 (5)	O4^v—Ca—O2	77.15 (5)
O5ⁱ—Ca—O4ⁱⁱⁱ	73.62 (5)	O1^iv—Ca—O2	79.00 (5)
O3ⁱⁱ—Ca—O4ⁱⁱⁱ	89.42 (5)	O3—Ca—O2	61.06 (5)
O5ⁱ—Ca—O2^iv	151.07 (5)	O5—Cu—O5^vi	177.68 (6)
O3ⁱⁱ—Ca—O2^iv	108.51 (6)	O5—Cu—O1^vi	98.01 (6)
O4ⁱⁱⁱ—Ca—O2^iv	77.79 (5)	O5^vi—Cu—O1^vi	84.26 (6)
O5ⁱ—Ca—O4^v	74.41 (5)	O5—Cu—O1	84.21 (6)
O3ⁱⁱ—Ca—O4^v	76.55 (5)	O5^vi—Cu—O1	93.52 (6)
O4ⁱⁱⁱ—Ca—O4^v	147.36 (3)	O1^vi—Cu—O1	177.66 (7)
O2^iv—Ca—O4^v	134.48 (5)	O5—Cu—O3^vii	91.88 (6)
O5ⁱ—Ca—O1^iv	141.59 (5)	O5^vi—Cu—O3^vii	88.82 (6)
O3ⁱⁱ—Ca—O1^iv	73.13 (5)	O1^vi—Cu—O3^vii	84.84 (6)
O4ⁱⁱⁱ—Ca—O1^iv	127.50 (5)	O1—Cu—O3^vii	95.85 (6)
O2^iv—Ca—O1^iv	62.85 (5)	O5—Cu—O4^viii	84.76 (6)
O4^v—Ca—O1^iv	76.76 (5)	O5^vi—Cu—O4^viii	94.77 (6)
O5ⁱ—Ca—O3	72.94 (5)	O1^vi—Cu—O4^viii	89.81 (6)
O3ⁱⁱ—Ca—O3	147.75 (2)	O1—Cu—O4^viii	89.67 (5)
O4ⁱⁱⁱ—Ca—O3	74.21 (5)	O3^vii—Cu—O4^viii	173.23 (6)
O2^iv—Ca—O3	95.19 (5)	O4—As—O3	113.27 (7)
O4^v—Ca—O3	102.41 (5)	O4—As—O2	115.43 (8)
O1^iv—Ca—O3	138.68 (5)	O3—As—O2	103.94 (8)
O5ⁱ—Ca—O2	117.86 (6)	O4—As—O1	108.94 (8)
O3ⁱⁱ—Ca—O2	145.22 (5)	O3—As—O1	112.45 (8)
O4ⁱⁱⁱ—Ca—O2	124.48 (5)	O2—As—O1	102.33 (7)
O2^iv—Ca—O2	75.44 (3)

Symmetry codes: (i) −x+1/2, −y+1, z−1/2; (ii) x+1/2, −y+3/2, −z; (iii) x, y+1, z; (iv) −x+1, y+1/2, −z+1/2; (v) x+1/2, −y+1/2, −z; (vi) −x, y−1/2, −z+1/2; (vii) x−1/2, −y+1/2, −z; (viii) −x+1/2, −y, z+1/2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O5—H1···O2^ix	0.86 (4)	1.91 (4)	2.678 (2)	149 (3)

Symmetry code: (ix) x−1, y, z.

Experimental details

Crystal data
Chemical formula	CaCu(AsO₄)(OH)
M_r	259.57
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	293
a, b, c (Å)	7.3822 (2), 5.8146 (2), 9.2136 (3)
V (Å³)	395.49 (2)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	15.03
Crystal size (mm)	0.06 × 0.05 × 0.04

Data collection
Diffractometer	Bruker APEX2 CCD diffractometer
Absorption correction	Multi-scan (TWINABS; Sheldrick, 2008)
T_min, T_max	0.492, 0.585
No. of measured, independent and observed [I > 2σ(I)] reflections	7088, 1602, 1487
R_int	0.023
(sin θ/λ)_max (Å⁻¹)	0.787

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.018, 0.038, 1.03
No. of reflections	1602
No. of parameters	79
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.63, −0.49
Absolute structure	Flack (1983), 644 Friedel pairs
Absolute structure parameter	0.00 (2)

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

Selected bond lengths (Å) top

Ca—O5ⁱ	2.3626 (13)	Cu—O5^vi	1.8855 (16)
Ca—O3ⁱⁱ	2.3995 (17)	Cu—O1^vi	2.0666 (16)
Ca—O4ⁱⁱⁱ	2.4818 (16)	Cu—O1	2.0688 (15)
Ca—O2^iv	2.5178 (17)	Cu—O3^vii	2.2976 (15)
Ca—O4^v	2.5281 (16)	Cu—O4^viii	2.3882 (14)
Ca—O1^iv	2.5462 (14)	As—O4	1.6749 (16)
Ca—O3	2.5786 (17)	As—O3	1.6779 (16)
Ca—O2	2.6264 (17)	As—O2	1.6796 (16)
Cu—O5	1.8850 (15)	As—O1	1.7099 (13)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O5—H1···O2^ix	0.86 (4)	1.91 (4)	2.678 (2)	149 (3)

Symmetry code: (ix) x−1, y, z.

Acknowledgements

The authors gratefully acknowledge support of this study by the RRUFF project.

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