Skip to main content Accessibility help

Davidlloydite, ideally Zn3(AsO4)2(H2O)4, a new arsenate mineral from the Tsumeb mine, Otjikoto (Oshikoto) region, Namibia: description and crystal structure

  • F.C. Hawthorne (a1), M. A. Cooper (a1), Y. A. Abdu (a1), N. A. Ball (a1), M. E. Back (a1) and K. T. Tait (a1)...


Davidlloydite, ideally Zn3(AsO4)2(H2O)4, is a new supergene mineral from the Tsumeb mine, Otjikoto (Oshikoto) region, Namibia. It occurs as elongated prisms (∼10:1 length-to-width ratio) that are flattened on {010}, and up to 100 × 20 × 10 μm in size. The crystals occur as aggregates (up to 500 μm across) of subparallel to slightly diverging prisms lying partly on and partly embedded in fine-grained calcioandyrobertsite. Crystals are prismatic along [001] and flattened on {010}, and show the forms {010} dominant and {100} subsidiary. Davidlloydite is colourless with a white streak and a vitreous lustre; it does not fluoresce under ultraviolet light. The cleavage is distinct on {010}, and no parting or twinning was observed. The Mohs hardness is 3 – 4. Davidlloydite is brittle with an irregular to hackly fracture. The calculated density is 3.661 g cm–3. Optical properties were measured with a Bloss spindle stage for the wavelength 590 nm using a gel filter. The indices of refraction are α = 1.671, β = 1.687, γ = 1.695, all ±0.002; the calculated birefringence is 0.024; 2Vobs = 65.4(6)°, 2Vcalc = 70°; the dispersion is r < v, weak; pleochroism was not observed. Davidlloydite is triclinic, space group P1, with a = 5.9756(4), b = 7.6002(5), c = 5.4471(4) Å, α = 84.2892(9), β = 90.4920(9), γ = 87.9958(9)°, V = 245.99(5) Å3, Z = 1 and a:b:c = 0.7861:1:0.7167. The seven strongest lines in the X-ray powder diffraction pattern [listed as d (Å), I, (hkl)] are as follows: 4.620, 100, (011, 10); 7.526, 71, (010); 2.974, 49, (200, 01); 3.253, 40, (021, 120); 2.701, 39, (10, 002, 1); 5.409, 37, (001); 2.810, 37, (210). Chemical analysis by electron microprobe gave As2O5 43.03, ZnO 37.95, CuO 5.65, H2O(calc) 13.27, sum 99.90 wt.%. The H2O content and the valence state of As were determined by crystal structure analysis. On the basis of 12 anions with H2O = 4 a.p.f.u., the empirical formula is (Zn2.53Cu0.39)Σ2.92As2.03O8(H2O)4.

The crystal structure of davidlloydite was solved by direct methods and refined to an R 1 index of 1.51% based on 1422 unique observed reflections collected on a three-circle rotating-anode (MoKα radiation) diffractometer equipped with multilayer optics and an APEX-II detector. In the structure of davidlloydite, sheets of corner-sharing (As5+O4) and (ZnO4) tetrahedra are linked by ZnO2(H2O)4 octahedra. The structure is related to that of parahopeite.


Corresponding author


Hide All
Abrahams, S.C. and Bernstein, J.L. (1966) Crystal structure of para magnetic ludlamite, Fe3(PO4)2·4(H2O), at 298ºK. Journal of Chemical Physics, 44, 22232229.
Bartelmehs, K.L., Bloss, F.D., Downs, R.T. and Birch, J.B. (1992) Excalibr II. Zeitschrift für Kristallographie, 199, 186196.
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.
Chao, G.Y. (1969) Refinement of the crystal structure of parahopeite. Zeitschrift für Kristallographie, 130, 261266.
Gaines, R.V., Skinner, H.C.W., Foord, E.E., Mason, B. and Rosenwieg, A. (1997) Dana’s New Mineralogy, Eighth Edition. Wiley and Sons, New York, USA.
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.
Hill, R.J. (1977) The crystal structure of phosphophyllite. American Mineralogist, 62, 812817.
Hill, R.J. and Jones, J.B. (1976) The crystal structure of hopeite. American Mineralogist, 61, 987995.
Kumbasar, I. and Finney, J.J. (1968) The crystal structure of parahopeite. Mineralogical Magazine, 36, 621624.
Neuhold, F., Kolitsch, U., Bernhardt, H.-J. and Lengauer, C.L. (2011) Arsenhopeite, IMA 2010-69. CNMNC Newsletter No. 8, April 2011, page 291; Mineralogical Magazine, 75, 289294.
Pinch, W.W. and Wilson, W.E. (1977) Tsumeb Minerals, V.: 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 (Armstrong, J.T., editor). San Francisco Press, San Francisco, California, USA.
Sarp, H. and Cerný , R. (2000) Rollandite, Cu3(AsO4)2·4H2O, a new mineral: its description and crystal structure. European Journal of Mineralogy, 12, 10451050.
Sheldrick, G.M. (2008) A short history of SHELX. Acta Crystallographica, A64, 112122.
Strunz, H. and Nickel, E.H. (2001) Strunz Mineralogical Tables, Ninth Edition. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany.
Weber, D. and Wilson, W.E. (1977) Tsumeb IV. Geology. Mineralogical Record, 8(3), 1416.


Type Description Title
Supplementary materials

Hawthorne et al. supplementary material
cif file

 Word (55 KB)
55 KB
Supplementary materials

Hawthorne et al. supplementary material
Structure factors

 Word (72 KB)
72 KB

Davidlloydite, ideally Zn3(AsO4)2(H2O)4, a new arsenate mineral from the Tsumeb mine, Otjikoto (Oshikoto) region, Namibia: description and crystal structure

  • F.C. Hawthorne (a1), M. A. Cooper (a1), Y. A. Abdu (a1), N. A. Ball (a1), M. E. Back (a1) and K. T. Tait (a1)...


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