| Reference Type | Journal (article/letter/editorial) |
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| Title | Davidlloydite, ideally Zn3(AsO4)2(H2O)4, a new arsenate mineral from the Tsumeb mine, Otjikoto (Oshikoto) region, Namibia: description and crystal structure |
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| Journal | Mineralogical Magazine |
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| Authors | Hawthorne, Frank C. | Author |
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| Cooper, Mark A. | Author |
| Abdu, Yassir A. | Author |
| Ball, Neil A. | Author |
| Back, Malcolm E. | Author |
| Tait, Kim T. | Author |
| Year | 2012 (February) | Volume | 76 |
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| Issue | 1 |
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| Publisher | Mineralogical Society |
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| Download URL | https://rruff.info/rruff_1.0/uploads/MM76_45.pdf+ |
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| DOI | doi:10.1180/minmag.2012.076.1.45Search in ResearchGate |
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| Generate Citation Formats |
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| Classification | Not set | LoC | Not set |
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| Mindat Ref. ID | 244212 | Long-form Identifier | mindat:1:5:244212:3 |
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| GUID | 0 |
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| Full Reference | Hawthorne, Frank C., Cooper, Mark A., Abdu, Yassir A., Ball, Neil A., Back, Malcolm E., Tait, Kim 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, 76 (1) 45-57 doi:10.1180/minmag.2012.076.1.45 |
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| Plain Text | Hawthorne, Frank C., Cooper, Mark A., Abdu, Yassir A., Ball, Neil A., Back, Malcolm E., Tait, Kim 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, 76 (1) 45-57 doi:10.1180/minmag.2012.076.1.45 |
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| In | (2012, February) Mineralogical Magazine Vol. 76 (1) Mineralogical Society |
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| Abstract/Notes | 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 R1 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. |
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