Crystal structure study of a cobaltoan dolomite from Kolwezi, Democratic Republic of Congo

A structural study has been undertaken on a cobaltoan dolomite, with chemical formula CaMg_0.83Co_0.17(CO₃)₂ (cal­cium magnesium cobalt dicarbonate), from Kolwezi, Democratic Republic of Congo. Pale-pink euhedral cobaltoan dolomite was associated with kolwezite [(Cu_1.33Co_0.67)(CO₃)(OH)₂] and cobaltoan malachite [(Cu,Co)₂(CO₃)(OH)₂]. A crystal with a Co:Mg ratio of 1:5.6 (SEM/EDAX measurement), twinned on (11 -2 0) was used for crystal structural refinement. The refinement of the structural model of Reeder & Wenk [Am. Mineral. (1983), 68, 769–776; Ca at site 3a with site symmetry -3; Mg site at site 3b with site symmetry -3; C at site 6c with site symmetry 3; O at site 18f with site symmetry 1] showed that Co is totally incorporated in the Mg site, with refined occupancy Mg_0.83Co_0.17, which compares with Mg_0.85Co_0.15 from chemical data. The Co substitution reflects in the expansion of the cell volume, with a pronounced increasing of the c cell parameter.

Key indicators

• Single-crystal X-ray study
• T = 295 K
• Mean [sigma](O-C) = 0.001 Å
• Disorder in main residue
• R factor = 0.019
• wR factor = 0.059
• Data-to-parameter ratio = 12.9

checkCIF/PLATON results

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Alert level C
PLAT077_ALERT_4_C Unitcell contains non-integer number of atoms ..     Please Check

Alert level G
PLAT004_ALERT_5_G Polymeric Structure Found with Maximum Dimension          2 Info
PLAT040_ALERT_1_G No H-atoms in this Carbon Containing Compound ..     Please Check
PLAT045_ALERT_1_G Calculated and Reported Z Differ by ............       0.33 Ratio
PLAT068_ALERT_1_G Reported F000 Differs from Calcd (or Missing)...     Please Check
PLAT152_ALERT_1_G The Supplied and Calc. Volume s.u. Differ by ...          2 Units
PLAT171_ALERT_4_G The CIF-Embedded .res File Contains EADP Records          1 Report
PLAT301_ALERT_3_G Main Residue  Disorder ............ Percentage =          8 Note
PLAT860_ALERT_3_G Number of Least-Squares Restraints .............          1 Note
PLAT870_ALERT_4_G ALERTS Related to Twinning Effects Suppressed ..          ! Info
PLAT912_ALERT_4_G Missing # of FCF Reflections Above STh/L=  0.600          5 Note
PLAT931_ALERT_5_G Found Twin Law ( 2-1  0)[       ] Estimated BASF       0.80 Check
PLAT961_ALERT_5_G Dataset Contains no Negative Intensities .......     Please Check

   0 ALERT level A = Most likely a serious problem - resolve or explain
   0 ALERT level B = A potentially serious problem, consider carefully
   1 ALERT level C = Check. Ensure it is not caused by an omission or oversight
  12 ALERT level G = General information/check it is not something unexpected

   4 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
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S1. Synthesis and crystallization

Cobaltoan dolomite was picked from a kolwezite sample from Kolwezi (inventory number RC 3987) kindly provided us by H. Goethals, Royal Belgian Institute for Natural Sciences, Brussels. Pale pink euhedral cobaltoan dolomite was associated with kolwezite and cobaltoan malachite. All these minerals occur in the supergene zones of Cu—Co sulfide ore deposits,originating from the alteration of primary sulphides such as carrollite,Cu(Co,Ni)₂As₄

S2. Refinement

During the refinement, the twinning according to the (1120) common law was detected and accounted for, with a refined BASF parameter of 0.798. The sum of Co and Mg occupancies in Mg site was constrained to be equal to 1, no other constraint was applied.

Related literature

For general background, see: Barton et al. (2015); Pertlik (1986). For isostructural/isotypic structures, see: Reeder & Wenk (1983). For kolwezite, see: Deliens & Piret (1980).

Computing details

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXS2014 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2008, 2015) and WinGX (Farrugia, 2012); molecular graphics: CrystalMaker (CrystalMaker, 2010); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures

	Fig. 1. Micro photograph of the cobaltoan dolomite specimen, where pale pink cobaltoan dolomite is associated with pale green cobaltoan malachite.
	Fig. 2. The crystal structure of cobaltoan dolomite, in a projection along [100], slightly tilted by 5° about along the x Cartesian rotation axis. Ca-centered octahedra are cyan, whereas Mg-centered octahedra are yellow; carbon and oxygen atoms are represented as green and red spheres, respectively.
	Fig. 3. Coordination polyhedra in cobaltoan dolomite. Displacement ellipsoids are drawn at the 50% probability.

Calcium magnesium cobalt dicarbonate

Crystal data

CaMg0.83Co0.17(CO3)2	F(000) = 284
Mr = 190.38	Dx = 2.930 Mg m^−3
Trigonal, R3	Mo Kα radiation, λ = 0.71073 Å
a = 4.8158 (1) Å	µ = 2.17 mm^−1
c = 16.0488 (6) Å	T = 295 K
V = 322.34 (2) Å^3	Cleavage rhombohedron, pale pink
Z = 3	0.2 × 0.15 × 0.12 mm

Data collection

Bruker SMART Breeze CCD diffractometer	257 reflections with I > 2σ(I)
ω scans	Rint = 0.010
Absorption correction: multi-scan (SADABS; Bruker, 2008)	θmax = 32.4°, θmin = 3.8°
Tmin = 0.621, Tmax = 0.746	h = −7→3
258 measured reflections	k = 0→7
738 independent reflections	l = −23→23

Refinement

Refinement on F^2	20 parameters
Least-squares matrix: full	1 restraint
R[F^2 > 2σ(F^2)] = 0.019	w = 1/[σ^2(Fo^2) + (0.0438P)^2 + 0.562P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.059	(Δ/σ)max < 0.001
S = 0.96	Δρmax = 0.46 e Å^−3
258 reflections	Δρmin = −0.32 e Å^−3

Special details

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. Refined as a 2-component twin.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ca1	0.0000	0.0000	0.0000	0.01249 (17)
Mg1	0.0000	0.0000	0.5000	0.0104 (3)	0.828 (4)
Co1	0.0000	0.0000	0.5000	0.0104 (3)	0.172 (4)
C1	0.0000	0.0000	0.24297 (12)	0.0106 (4)
O1	0.2482 (2)	−0.0341 (2)	0.24403 (6)	0.0143 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ca1	0.0121 (2)	0.0121 (2)	0.0133 (3)	0.00605 (10)	0.000	0.000
Mg1	0.0091 (3)	0.0091 (3)	0.0130 (4)	0.00456 (15)	0.000	0.000
Co1	0.0091 (3)	0.0091 (3)	0.0130 (4)	0.00456 (15)	0.000	0.000
C1	0.0103 (5)	0.0103 (5)	0.0112 (8)	0.0051 (3)	0.000	0.000
O1	0.0117 (4)	0.0156 (4)	0.0183 (4)	0.0088 (3)	−0.0024 (3)	−0.0033 (3)

Geometric parameters (Å, º)

Ca1—O1^i	2.3833 (10)	Mg1—O1^ix	2.0923 (9)
Ca1—O1^ii	2.3833 (10)	Mg1—O1^x	2.0923 (9)
Ca1—O1^iii	2.3833 (10)	Mg1—O1^xi	2.0923 (9)
Ca1—O1^iv	2.3833 (10)	Mg1—O1^xii	2.0923 (9)
Ca1—O1^v	2.3833 (10)	C1—O1	1.2853 (9)
Ca1—O1^vi	2.3833 (10)	C1—O1^xiii	1.2853 (9)
Mg1—O1^vii	2.0923 (9)	C1—O1^xiv	1.2853 (9)
Mg1—O1^viii	2.0923 (9)	C1—Ca1^xv	3.1359 (9)
O1^i—Ca1—O1^ii	180.00 (5)	O1^viii—Mg1—O1^ix	91.62 (4)
O1^i—Ca1—O1^iii	92.43 (3)	O1^vii—Mg1—O1^x	91.62 (4)
O1^ii—Ca1—O1^iii	87.57 (3)	O1^viii—Mg1—O1^x	88.38 (4)
O1^i—Ca1—O1^iv	87.57 (3)	O1^ix—Mg1—O1^x	180.0
O1^ii—Ca1—O1^iv	92.43 (3)	O1^vii—Mg1—O1^xi	91.62 (4)
O1^iii—Ca1—O1^iv	180.00 (4)	O1^viii—Mg1—O1^xi	88.38 (4)
O1^i—Ca1—O1^v	87.57 (3)	O1^ix—Mg1—O1^xi	91.62 (4)
O1^ii—Ca1—O1^v	92.43 (3)	O1^x—Mg1—O1^xi	88.38 (4)
O1^iii—Ca1—O1^v	92.43 (3)	O1^vii—Mg1—O1^xii	88.38 (4)
O1^iv—Ca1—O1^v	87.57 (3)	O1^viii—Mg1—O1^xii	91.62 (4)
O1^i—Ca1—O1^vi	92.43 (3)	O1^ix—Mg1—O1^xii	88.38 (4)
O1^ii—Ca1—O1^vi	87.57 (3)	O1^x—Mg1—O1^xii	91.62 (4)
O1^iii—Ca1—O1^vi	87.57 (3)	O1^xi—Mg1—O1^xii	180.00 (4)
O1^iv—Ca1—O1^vi	92.43 (3)	O1—C1—O1^xiii	119.984 (5)
O1^v—Ca1—O1^vi	180.00 (8)	O1—C1—O1^xiv	119.983 (5)
O1^vii—Mg1—O1^viii	180.0	O1^xiii—C1—O1^xiv	119.981 (5)
O1^vii—Mg1—O1^ix	88.38 (4)

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