Skip to main content Accessibility help
×
Home

Ianbruceite, ideally [Zn2(OH)(H2O)(AsO4)](H2O)2, a new arsenate mineral from the Tsumeb mine, Otjikoto (Oshikoto) region, Namibia: description and crystal structure

  • M. A. Cooper (a1), Y. A. Abdu (a1), N. A. Ball (a1), F. C. Hawthorne (a1), M. E. Back (a2), K. T. Tait (a2), J. Schlüter (a3), T. Malcherek (a3), D. Pohl (a3) and G. Gebhard (a4)...

Abstract

Ianbruceite, ideally [Zn2(OH)(H2O)(AsO4)](H2O)2, is a new supergene mineral from the Tsumeb mine, Otjikoto (Oshikoto) region, Namibia. It occurs as thin platy crystals up to 80 μm long and a few μm thick, which form flattened aggregates up to 0.10 mm across, and ellipsoidal aggregates up to 0.5 mm across. It is associated with coarse white leiteite, dark blue köttigite, minor legrandite and adamite. Ianbruceite is sky blue to very pale blue with a white streak and a vitreous lustre; it does not fluoresce under ultraviolet light. It has perfect cleavage parallel to (100), is flexible, and deforms plastically. The Mohs hardness is 1 and the calculated density is 3.197 g cm-3. The refractive indices are α = 1.601, β = 1.660, γ = 1.662, all ±0.002; 2Vobs = 18(2)°, 2Vcalc = 20°, and the dispersion is r < v, weak. Ianbruceite is monoclinic, space group P21/c, a = 11.793(2), b = 9.1138(14), c = 6.8265(10) Å, β = 103.859(9)°, V = 712.3(3) Å3, Z = 4, a:b:c = 1.2940:1:0.7490. The seven strongest lines in the X-ray powder diffraction pattern [d(Å), I, (hkl)] are as follows: 11.29, 100, (100); 2.922, 17, (130); 3.143, 15, (202); 3.744, 11, (300); 2.655, 9, (230); 1.598, 8, (152); 2.252, 7, (222). Chemical analysis by electron microprobe gave As2O5 36.27, As2O3 1.26, Al2O3 0.37, ZnO 49.72, MnO 0.32, FeO 0.71, K2O 0.25, H2Ocalc 19.89, sum 108.79 wt.%; the very high oxide sum is due to the fact that the calculated H2O content is determined from crystal-structure analysis, but H2O is lost under vacuum in the electron microprobe.

The crystal structure of ianbruceite was solved by direct methods and refined to an R 1 index of 8.6%. The As is tetrahedrally coordinated by four O anions with a mean As O distance of 1.687 Å. Zigzag [[5]Zn[6]Znϕ7] chains extend in the c direction and are linked in the b direction by sharing corners with (AsO4) tetrahedra to form slabs with a composition [Zn2(OH)(H2O)(AsO4)]. The space between these slabs is filled with disordered (H2O) groups and minor lone-pair stereoactive As3+. The ideal formula derived from chemical analysis and crystal-structure solution and refinement is [Zn2(OH)(H2O)(AsO4)](H2O)2.

Copyright

Corresponding author

References

Hide All
Brown, I.D. and Altermatt, D. (1985) Bond-valence parameters obtained from a systematic analysis of the inorganic crystal structure database. Acta Crystallographica, B41, 244247.
Gebhard, G. (1999) Tsumeb - A Unique Mineral Locality. GG Publishing, Grossenseifen, Germany.
Hawthorne, F.C. (1976a) Refinement of the crystal structure of adamite. The Canadian Mineralogist, 14, 143148.
Hawthorne, F.C. (1976b) The hydrogen positions in scorodite. Acta Crystallographica, B32, 28912892.
Hawthorne, F.C. (1985) Towards a structural classification of minerals: The VIMIVT2jn minerals. American Mineralogist, 70, 455473.
Hawthorne, F.C. (1990) Structural hierarchy in [6]M[4] Tjnminerals . Zeitschrift für Kristallographie, 192, 152.
Hawthorne, F.C. (1992) The role of OH and H2O in oxide and oxysalt minerals. Zeitschrift fü r Kristallographie, 201, 183206.
Hawthorne, F.C. (1997) Short-range order in amphiboles: a bond-valence approach. The Canadian Mineralogist, 35, 201216.
Hawthorne, F.C., Cooper, M.A., Abdu, Y.A., Ball , N.A., Back, M.E. and Tait, K.T. (2012) Davidlloydite, ideally Zn3(AsO4)2(H2O)4, a new arsenate mineral from the Tsumeb mine, Otjikoto (Oshikoto) region, Namibia: description and crystal structure. Mineralogical Magazine, 77, 4557.
Hill, R.J. (1979) The crystal structure of kö ttigite. American Mineralogist, 64, 376382.
Keller, P. (1977) Tsumeb VI. Paragenesis. Mineralogical Record, 8(3), 3847.
Keller, P., Hess, H. and Riffel, H. (1980) Die Kristallstruktur von Koritnigit Zn((H2O) (OH)(AsO3)). Neues Jahrbuch für Mineralogie Abhandlungen, 138, 316332.
McLean, W.J., Anthony, J.W., Finney, J.J. and Laughon, R.B. (1971) The crystal structure of legrandite. American Mineralogist, 56, 11471154.
Neuhold, F., Kolitsch, U., Bernhardt, H.-J. and Lengauer, C.L. (2011) Arsenohopeite, a new zinc arsenate mineral from the Tsumeb mine, Namibia. Mineralogical Magazine, 76, 603612.
Petříček, V. and Dušek, M. (2000) Jana 98 The Crystallographic Computing System. Institute of Physics, Academy of Sciences of the Czech Republic, Praha.
Pinch, W.W. and Wilson, W.E. (1977) Tsumeb V. Minerals: a descriptive list. Mineralogical Record, 8(3), 1737.
Pouchou, J.L. and Pichoir, F. (1985) ‘PAP’ j(rZ) procedure for improved quantitative microanalysis. Pp. 104106 in: Microbeam Analysis (J.T. Armstrong, editor). San Francisco Press, San Francisco, California, USA.
Pushcharovskii, D.Y.., Pobedimskaya, E.A. and Belov, N.V. (1971) The crystal structure of legrandite Zn2(AsO4)OH(H2O). Doklady Akademii Nauk SSSR, 198, 10721075.
Riffel, H., Keller, P. and Hess, H. (1980) Die Kristallstruktur von Warikahnit, Zn3((H2O)2(AsO4)2). Tschermaks Mineralogische und Petrographische Mitteilungen, 27, 187199.
Sheldrick, G.M. (2008) A short history of SHELX. Acta Crystallographica, A64, 112122.
Weber, D. and Wilson, W.E. (1977) Tsumeb IV. Geology. Mineralogical Record, 8(3), 1416.

Keywords

Type Description Title
WORD
Supplementary materials

Cooper et al. supplementary material
Lambrucite cif

 Word (50 KB)
50 KB
WORD
Supplementary materials

Cooper et al. supplementary material
Lambrucite structure factors

 Word (63 KB)
63 KB

Metrics

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed