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Hereroite and vladkrivovichevite: two novel lead oxychlorides from the Kombat mine, Namibia

Published online by Cambridge University Press:  05 July 2018

R. Turner ,
O. I. Siidra ,
M. S. Rumsey ,
S. V. Krivovichev ,
C. J. Stanley  and
J. Spratt
R. Turner*
Affiliation:
The Drey, Allington Track, Allington, Salisbury SP4 0DD, UK
O. I. Siidra
Affiliation:
Department of Crystallography, Geological Faculty, Saint-Petersburg State University, University emb. 7/9, St Petersburg 199034, Russia
M. S. Rumsey
Affiliation:
Earth Sciences Department, Natural History Museum, Cromwell Road, London SW7 5BD, UK
S. V. Krivovichev
Affiliation:
Department of Crystallography, Geological Faculty, Saint-Petersburg State University, University emb. 7/9, St Petersburg 199034, Russia
C. J. Stanley
Affiliation:
Earth Sciences Department, Natural History Museum, Cromwell Road, London SW7 5BD, UK
J. Spratt
Affiliation:
Earth Sciences Department, Natural History Museum, Cromwell Road, London SW7 5BD, UK
*
*E-mail: [email protected]
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Abstract

Two new lead oxychloride minerals, hereroite [Pb32(O, ☐)21](AsO4)2((Si,As,V,Mo)O4)2Cl10 and vladkrivovichevite [Pb32O18][Pb4Mn2O]Cl14(BO3)8·2H2O occur in association with asisite, damaraite, kombatite, sahlinite, copper, quartz, barysilite, Mn silicates and a number of Mn oxyhydroxide minerals on a specimen from the Kombat mine in Namibia. The minerals formed as late-stage products of hydrothermal reworking of primary sulfide minerals.

Hereroite is monoclinic, C2/c with a = 23.14(1), b = 22.65(1), c = 12.39(1) Å, β = 102.00(5)°, V = 6351.6(41) Å3 from powder-diffraction data and a = 23.139(4), b = 22.684(4), c = 12.389(2) Å, β = 102.090(3)°, V = 6358.8(18) Å3 from single-crystal data. It is bright orange, with white streak and adamantine lustre. It is brittle with no observed parting or cleavage and has a conchoidal fracture. The calculated density is 8.15 g cm–3. The mean refractive index in air at 589 nm is 2.38. The six strongest reflections in the X-ray powder diffraction pattern [d in Å, (I), (hkl)] are as follows: 2.982(100)(51); 2.795(47)(80); 1.986(24)(8); 1.641(24)(11..); 3.512(23)(61); 3.901(21)(511). Hereroite is named for the Herero people, one of the indigenous tribal groupings in the region where the Kombat mine is located.

Vladkrivovichevite is orthorhombic, Pmmn with a = 12.87(5), b = 27.7(4), c = 11.46(3) Å, V = 4080.1(5) Å3, from powder-diffraction data and a = 12.759(1), b = 27.169(4), c = 11.515(1) Å, V = 3992.0(9) Å3, Z = 2, from single-crystal data. It is pale greenish yellow, with white streak and adamantine lustre. It is brittle with no observed parting or cleavage and has a conchoidal fracture. The calculated density is 7.40 g cm–3. The mean refractive indices in air at 589 nm are 2.30 and 2.34. The six strongest reflections in the X-ray powder diffraction pattern [d in Å, (I), (hkl)] are as follows: 2.860(100)(370); 2.733(84)(073); 3.707(49)(073); 3.068(37)(401); 2.075(32)(473); 1.601(32)(3.14.3). Vladkrivovichevite is named in honour of Prof. Dr Vladimir Gerasimovich Krivovichev (b. 24.04.1946), Head of the Department of Mineralogy, Geological Faculty, St Petersburg State University.

The crystal structures of hereroite and vladkrivovichevite consist of alternating litharge-like O – Pb double layers and chlorine sheets and both are structurally related to other layered lead oxychlorides. In hereroite, tetrahedral AsO4 and (Si, As, V, Mo)O4 groups locate in defects within the O – Pb block, which combines square 'symesite-type' and double-square 'kombatite-type' cavities in its crystal structure. The structure of vladkrivovichevite is based on O – Pb derivative blocks with the interlayer occupied by Cl– anions and oxocentred OPb4Mn2 octahedra whose eight triangular faces are capped by triangular borate anions, BO33–.

Keywords

hereroitevladkrivovicheviteKombat minelayered lead oxychlorideslead oxyhalidesnamibianew mineral speciesnew structuresOPb4 tetrahedraoxocentred units
Type
Research Article
Information
Mineralogical Magazine , Volume 76 , Issue 4 , August 2012 , pp. 883 - 890
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2012

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