Tsumeb Mine Research Articles

GEOLOGISTS AS COLONIAL SCOUTS: THE ROGERS EXPEDITION TO OTAVI AND TSUMEB, NAMIBIA, 1892–1895

ABSTRACT From 1892 to 1895, the South West Africa Company (SWACO) expedition led by geologist Matthew Rogers conducted the first geologic mapping in Namibia’s Otavi Mountains, including the now world-famous Tsumeb Mine. This paper uses archival documents from the Rogers expedition to trace his geologic contributions and to illustrate important themes in the relationships between 19th century colonial geologists, Western colonizing governments, Indigenous communities, resource extraction, and corporations. To carry out his mapping, Rogers performed a continuous balancing act between British and German colonial powers and local African leaders. The local leaders and communities he interacted with variously resisted his incursions, or collaborated with him, but consistently and vocally asserted their rights to the land and copper in Otavi. In addition to geologic mapping, Rogers understood his role as intelligence gatherer, reporting back on the resources needed to facilitate European settlers in the region, including his views on how Germany might subjugate local communities and ensure their labor for the growing colony. Throughout, the expedition was dependent on African guides to keep them alive and show them where copper outcropped, yet Rogers’ letters back to SWACO promoted racial and cultural prejudices that became the foundations for how SWACO would interact with those communities in the future. In addition to laying the geologic groundwork for the Otavi area, the expedition illustrated the many roles that 19th century colonial geologists played in Western colonization.

Conservation of the Shaft #1 Headgear at the Tsumeb Mine, Namibia: Corrosion Protection

ABSTRACT The Tsumeb Mine in Namibia represents one of the best-preserved mining sites in the world and is rapidly gaining cross-disciplinary interest among cultural and engineering scientists. Most of the open pit and the shaft mining equipment are still in place, including the ore processing units and the local power plant. The mining area thus deserves recognition as an industrial world heritage site, especially due to the rarity of such locations on the African continent. The Shaft #1 headgear, built in 1924, represents one of the oldest known riveted steel headgears of the Promnitz design worldwide. In contrast to similar steel structures located in the northern hemisphere, it has been exposed to a different rural semi-arid climate since it is located in the Otavi Mountain Land, characterized by semi-annual change of rainy and dry seasons. Parts of the Shaft #1 headgear have remained largely untouched for more than 70 years. Besides its outstanding heritage value, it thus also represents an interesting object for studying the composition of corrosion layers formed on mild steel surfaces when exposed to continental and industrial mining atmospheres. To find a suitable transparent corrosion prevention coating, various on-site coating samples were evaluated after 11 months of outdoor exposure, including Owatrol Oil®, which is based on natural oil and alkyd resin with strong wicking potential. The substance is frequently applied for the conservation of single components but is not yet widely used on large steel structures in the field of industrial heritage conservation. However, it represented the most stable anti-corrosion coating under the local atmospheric conditions in the on-site tests. Thus, the suitability of Owatrol Oil® as a transparent coating for corrosion protection of riveted mild steel structures in such climates was further investigated as a more recent approach for the conservation of large steel structures. Since the protective coatings are exposed to strong UV radiation in the local climate, the addition of a specific UV stabilizer mixture was also tested. For such laboratory tests, two mild steel samples were taken. The first one originated from a diagonal strut of the 1920s and the second one from a handrail mounted in the early 1960s. Using corresponding high-resolution scanning electron microscopy (HR-SEM) and energy-dispersive X-ray spectroscopy (EDX) it was found that the corrosion layers are predominantly composed of lepidocrocite and goethite. A weathering program simulating the specific environmental conditions at Tsumeb in a UV climate chamber was developed and the corrosion resistance of the mild steel surface was subsequently evaluated by potentiodynamic measurements. Such tests proved to be a fast and reliable procedure for ranking the corrosion resistance of the old mild steels. It was found that the long-term corrosion layers already provide significant protection against further corrosion in the simulated environment. However, the study also showed that this can be further improved by the application of the Owatrol Oil® as a protective coating that also seals crevices. The addition of the UV stabilizers, however, led to a significant deterioration in corrosion protection, even in comparison to that of the uncoated long-term corrosion layers on the surface. Regular overcoating seems more advisable for the long-term preservation of the Shaft #1 headgear than modifying the Owatrol Oil® coating with the tested UV-stabilizing additives.

Wulfenite from Tsumeb, Namibia

Map prepared by William Besse.The Tsumeb mine, in northern Namibia, according to Moore (2016, p. 709), is one of the world's few “first-rank” localities for wulfenite outside of Mexico and Arizona ...

Connoisseur's Choice: Duftite after Wulfenite, Tsumeb Mine, Namibia

Tsumeb wulfenite is world-famous (see Southwood, this issue). Equally well-known among Tsumeb aficionados, but likely not as famous, are the pseudomorphs after wulfenite from the Tsumeb mine. One o...

The Where of Mineral Names: Tsumebite, Tsumeb Mine, Namibia

Tsumeb is the world's greatest mineral locality according to Wilson (1977). It is credited with 288 valid minerals and no less than 72 type-locality species, some of which occur only there (Mindat....

Munakataite, Pb2Cu2(Se4+O3)(SO4)(OH)4, and Other Selenium Minerals from Tsumeb, Namibia

The occurrence of munakataite, a rare lead-copper selenite, is reported from the Tsumeb mine, in Namibia, for the first time (fig. 1). It occurs in association with other rare minerals that contain...

Dolomite “Casts” and Epimorphs From Tsumeb, Namibia

For most mineral enthusiasts the Tsumeb mine, in northern Namibia (fig. 1), needs no introduction. More than 280 valid mineral species have been recorded from Tsumeb, which is the type locality for...

Connoisseur's Choice: Reinerite, Tsumeb, Namibia

The Tsumeb mine in northern Namibia is renowned for its wide assortment of secondary minerals, many of which occur as abundant, large, and colorful crystals that grace collections worldwide; others...

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

AbstractIanbruceite, 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 isr<v, weak. Ianbruceite is monoclinic, space groupP21/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 As2O536.27, As2O31.26, Al2O30.37, ZnO 49.72, MnO 0.32, FeO 0.71, K2O 0.25, H2Ocalc19.89, 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 anR1index 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 thecdirection and are linked in thebdirection 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.

Refinement of the crystal structure of zoned philipsbornite–hidalgoite from the Tsumeb mine, Namibia, and hydrogen bonding in the D2+G3+3(T5+O4)(TO3OH)(OH)6 alunite structures

AbstractThe crystal structure of zoned philipsbornite – hidalgoite, hexagonal (rhombohedral), Rm , Z = 3: a = 7.1142(4), c = 17.0973(9) A ˚ , V = 749.4(1) Å3, from the Tsumeb mine, Namibia, has been refined to R1 = 1.68% for 301 unique reflections collected on a Bruker D8 three-circle diffractometer equipped with a rotating-anode generator, multilayer optics and an APEX-II CCD detector. Chemical analysis by electron microprobe showed zoned crystals with a rim enriched in S and Fe relative to the core. The core composition is SO3 3.31, As2O5 30.57, Al2O3 23.05, FeO 1.44, PbO 33.94, H2Ocalc 9.58, total 101.79 wt.%, corresponding to Pb0.982+(Al2.92Fe0.132+)(AsO4)[(As0.72S0.27)O3.14(OH)0.85](OH)6; and the rim composition is SO3 8.88, As2O5 22.63, Al2O3 22.90, FeO 2.57, PbO 34.91, H2Ocalc 9.27, total 101.16 wt.%, corresponding to Pb0.992+(Al2.85Fe0.232+)(AsO4)[(As0.25S0.70)O3.30(OH)0.50](OH)6. Philipsbornite – hidalgoite has the alunite-type structure, sheets of corner-sharing octahedra, decorated on top and bottom by [(As,S)O4] and (AsO3OH) tetrahedra, that are linked into a three-dimensional structure by [12]-coordinated Pb2+ cations and hydrogen bonds. A new hydrogen-bonding scheme for the D2+G33+(T5+O4)(TO3OH)(OH)6 minerals is proposed.

Arsenohopeite, a new zinc arsenate mineral from the Tsumeb mine, Namibia

AbstractArsenohopeite, ideally Zn3(AsO4)2·4H2O, is the arsenate analogue of hopeite, Zn3(PO4)2·4H2O (it is isostructural with α-hopeite). It was found as a single colourless to blue crystalline grain from the Tsumeb mine, Namibia. The holotype specimen is ∼1 × 1 × 1 mm in size. Arsenohopeite is associated with tiny white fibres of an unidentified Zn- and As-bearing phase. It is orthorhombic, space group Pnma, with a = 10.804(2), b = 19.003(4), c = 5.112(1) Å, V = 1049.5(4) Å3 and Z = 4. Electron microprobe analysis yielded: ZnO 44.92, Fe2O3 0.92, MnO 0.51, MgO 0.20, CuO 0.02, As2O5 45.84 (wt.%). The empirical formula is (Zn2.80Fe0.06Mn0.04Mg0.03)Σ2.93(As1.01O4)2·4H2O, based on 12 oxygen atoms. Optically, the mineral is biaxial negative, with α = 1.598(2), β = 1.606(2), γ = 1.613(2) (white light) and 2Vcalc = 86°. It is not pleochroic or fluorescent. Arsenohopeite is translucent with a vitreous lustre. It is brittle, has an uneven fracture and (by analogy with hopeite) a cleavage that is perfect on {010}, good on {100} and poor on {001}. The calculated density is 3.420 g cm–3. The five strongest calculated powder diffraction lines are [d in Å (I)(hkl)]: 9.502 (100)(020), 2.926 (95)(241), 4.937 (50)(011), 4.110 (48)(230) and 3.567 (31)(240). The crystal structure of arsenohopeite has been solved by direct methods and refined in space group Pnma to R1 = 0.0353. Raman spectroscopy confirms the crystal-structure data and indicates the presence of weak hydrogen bonds.

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

AbstractDavidlloydite, 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.

Plumboselite, Pb3O2(SeO3), a new oxidation-zone mineral from Tsumeb, Namibia

Plumboselite, ideally Pb3O2(SeO3), is a new selenite (IMA2010–028) from the Tsumeb mine, Namibia. It occurs as fibres on clausthalite and is also associated with smithsonite, mimetite and vaterite. Plumboselite occurs in subparallel to divergent clusters of thin, flattened, colourless fibres up to 0.3 mm in length, but not exceeding 5 μm in width and 2 μm in thickness. The fibres are elongated parallel to [001] and flattened on {010}, with {010} the only form observed. The crystals have a dull to adamantine lustre and a white streak. The tenacity is brittle and the Mohs hardness is estimated to be between 2 and 3. Plumboselite crystals are optically biaxial with parallel extinction and are length fast in all orientations. The Gladstone-Dale relationship predicts nav = 2.115. The high indices of refraction and small crystal size prevented the determination of other optical properties. The calculated density is 7.814 g/cm3. The empirical formula (based on 5 O atoms) is Pb2.92Ca0.01Se1.03O5. Plumboselite is orthorhombic, space group Cmc21, a = 10.5384(11), b = 10.7452(13), c = 5.7577(7) A, V = 651.98(12) A3 and Z = 4. The five strongest lines in the powder X-ray diffraction pattern are [dobs in A/(I)/hkl]: 3.155/(100)/221; 1.956/(26)/042,402; 2.886/(22)/311,002; 1.713/(21)/223; 2.691/(17)/040. The crystal structure was solved from single-crystal X-ray diffraction data and refined to R1 = 0.0371 on the basis of 200 unique reflections with Fo > 4σF. The structure is based on double [O2Pb3] chains of edge-sharing oxo-centered [OPb4] tetrahedra along c, between which are sited SeO3 triangles. The two independent Pb2+ atoms and the Se4+ atom have sterochemically active lone electron pairs.

Krieselite, Al2GeO4(F,OH)2: A new mineral from the Tsumeb mine, Namibia, representing the Ge analogue of topaz

Krieselite, Al2GeO4(F,OH)2: A new mineral from the Tsumeb mine, Namibia, representing the Ge analogue of topaz

New Mineral Names

Other| October 01, 2008 New Mineral Names* Paula C. Piilonen; Paula C. Piilonen † 1Mineral Sciences Division, Canadian Museum of Nature, P.O. Box 3443, Station D, Ottawa, Ontario K1P 6P4, Canada †E-mail: ppiilonen@mus-nature.ca Search for other works by this author on: GSW Google Scholar Glenn Poirier; Glenn Poirier 1Mineral Sciences Division, Canadian Museum of Nature, P.O. Box 3443, Station D, Ottawa, Ontario K1P 6P4, Canada Search for other works by this author on: GSW Google Scholar Kimberly T. Tait Kimberly T. Tait 2Department of Natural History, Royal Ontario Museum, 100 Queen’s Park, Toronto, Ontario M5S 2C6, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information Paula C. Piilonen † 1Mineral Sciences Division, Canadian Museum of Nature, P.O. Box 3443, Station D, Ottawa, Ontario K1P 6P4, Canada Glenn Poirier 1Mineral Sciences Division, Canadian Museum of Nature, P.O. Box 3443, Station D, Ottawa, Ontario K1P 6P4, Canada Kimberly T. Tait 2Department of Natural History, Royal Ontario Museum, 100 Queen’s Park, Toronto, Ontario M5S 2C6, Canada †E-mail: ppiilonen@mus-nature.ca Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online ISSN: 1945-3027 Print ISSN: 0003-004X © 2008 American Mineralogist American Mineralogist (2008) 93 (10): 1686–1691. https://doi.org/10.2138/am.2008.527 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Paula C. Piilonen, Glenn Poirier, Kimberly T. Tait; New Mineral Names. American Mineralogist 2008;; 93 (10): 1686–1691. doi: https://doi.org/10.2138/am.2008.527 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search J.L. Jambor, A.C. Roberts, L.A. Groat, C.J. Stanley, A.J. Criddle, and M.N. Feinglos (2007) Calvertite, Cu5Ge0.5S4 , a new mineral species from Tsumeb, Namibia. Can. Mineral., 45, 1519–1523. Calvertite was discovered during the examination of another new mineral (gallobeaudanite) from the Tsumeb mine. The un-oxidized portions of the sample in which calvertite was found consist mainly of calvertite and reinerite with minor tennantite and gallite inclusions. Calvertite occurs in a granular texture formed by a network of chalcocite veins. The calvertite grains are anhedral, elongate to elliptical with the largest grains up to 100 μm... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

CALVERTITE, Cu5Ge0.5S4, A NEW MINERAL SPECIES FROM TSUMEB, NAMIBIA

The sulfide-rich matrix of a partly oxidized specimen from the Tsumeb mine, Tsumeb, Namibia, consists mainly of renierite, tennantite, gallite, chalcocite, and the new mineral calvertite, simplified as Cu 5 Ge 0.5 S 4 , which is named after Lauriston D. Calvert (1924–1993) of the National Research Council, Ottawa, Canada. Calvertite occurs as anhedral grains, up to 100 μm across, that are outlined by a network of chalcocite veinlets of micrometric width. In reflected light, calvertite is opaque, pale bluish grey, and isotropic. Reflectance percentages in air are 26.3 (470 nm), 23.1 (546), 22.2 (589), and 21.5% (650). The mineral is brittle, macroscopically black with a black streak, and has a hardness of 4 to 5, a conchoidal to uneven fracture, and no cleavage. Single-crystal X-ray study indicated F -centered cubic symmetry, a 5.337(3) A; the structure has not been solved, and the powder-diffraction pattern has only four lines [ d in A( I )( hkl )]: 3.053(100)(111), 2.639(10)(200), 1.869(90)(220), and 1.595(30) (311). An electron-microprobe analysis gave Cu 63.10, Fe 1.66, Zn 0.55, Ge 5.76, As 1.50, Ga 0.36, V 0.05, S 26.63, total 99.60 wt.%, corresponding to (Cu 4.782 Fe 0.143 Zn 0.041 Ga 0.025 V 0.005 ) S4.996 (Ge 0.382 As 0.096 ) S0.478 S 4 on the basis of S = 4 atoms and Z = 1. It is likely that the structure is disordered, and the measured unit-cell is the subcell of a compound whose ordered equivalent has the simplified formula Cu 10 GeS 8 .

Calcio-andyrobertsite-2O, KCaCu5(AsO4)4[AsO2(OH)2]2H2O: its description, crystal structure and relation with calcio-andyrobertsite-1M

Calcio-andyrobertsite-2O, ideally, CaCu5AsO4[AsO4(AsO2] • 2H2O, is a polytype of calcio-andyrobertsite-1 M, and occurs in a specimen of quartz gangue found at the Tsumeb mine, Namibia, together with cuprian adamite. It forms platy crystals with a maximum dimension of 7 × 3 × 0.5 mm. The intense blue crystals are elongated along [011] or [001], platy on {100}, and have a good cleavage on {100} and conchoidal fracture. They are not twinned. The mineral is orthorhombic, Pnma, a = 19.647(2), b, = 10.087(1), c = 9.963(1) A, V = 1974.4(4) A3, Z = 4, Dmeas= 3.9(1) and Dcalc= 3.80(1) g/cm3. The strongest lines in the X-ray powder diffraction pattern (dobs in A, (hkl), Ivis) are: 9.80, (200), 50; 7.084, (011), 70; 6.665, (111), 60; 4.830, (102), 70; 4.487, (220), 90; 3.965, (302), 60; 3.116, (322)(610), 100; 2.760, (132), 90; 2.674, (431), 40; 1.758, (840)(11.01), 40. Mohs' hardness is 3 to 4. Lustre is vitreous, streak is pale blue; crystals are transparent and biaxial (−) with α = 1.715(5), β = 1.730(5), γ = 1.735(5) at 589 nm; 2Vobs= 55(5)°, 2Vcalc = 60(3)°. Pleochroism is moderate with γ = intense blue, β = blue, α = pale blue. The crystal structure was solved by direct methods (single crystal, MoKα radiation) and refined using all 1911 observed unique reflections to R(F) = 0.039, wR(F)=0.105..

Tsumgallite, GaO(OH), a new mineral from the Tsumeb mine, Tsumeb, Namibia

The new mineral tsumgallite is a gallium oxide hydroxide, has the ideal chemical formular GaO(OH), is orthorhombic, space group Pbnm, with a = 4.512(5) A, b = 9.772(8) A, c = 2.967(4) A, cell volume 130.8(2) A 3 , Z = 4, from powder data. Cell parameter refined from powder data with the structure of α-gallium oxide deuteriohydroxide give a = 4.517 A, b = 9.760 A, c = 2.964 A, volume 130.7 A 3 . Tsumgallite is isostructural to goethite and diaspore. The strongest reflections in the X-ray powder diffraction data are as follows: (d m e a s . (A),I,(hkl)): 4.089(100)(110), 2.404(100)(111), 2.632(33)(130), 1.690(26)(221) and 2.530(22) (021). Tsumgallite was found at the Tsumeb mine, Tsumeb, Namibia. It forms tiny mica-like aggregates less than 1 mm across. Individual thin, platy crystals do not exceed 40 μm in size. The colour is a pale greenish yellow to beige. Tsumgallite is associated with of sohngeite and zincian siderite in vugs of a tennantite-germanite ore. Chemical analyses by electron microprobe gave Ga 2 O 3 78.13, Fe 2 O 3 3.99, GeO 2 4.01, ZnO 0.78, SiO 2 1.07, H 2 O ( i d e a l ) 8.77, sum 96,75 weight %, where the amount of water was taken from the ideal composition. The resulting empirical formular calculated on the basis of 2 anions is (Ga 0 . 8 6 , Fe 3 + 0.05, Ge 0 . 0 4 , Si 0 . 0 2 , Zn 0 . 0 1 ) Σ 0 . 9 8 O(OH) 1 . 0 1 . The mineral was named for the type locality and its chemical composition. Tsumgallite has been approved by the I.M.A. Commission on New Minerals and Mineral Names.

SEWARDITE, CaFe3+2(AsO4)2(OH)2, THE Ca-ANALOGUE OF CARMINITE, FROM TSUMEB, NAMIBIA: DESCRIPTION AND CRYSTAL STRUCTURE

Sewardite, ideally CaFe 3+ 2 (AsO 4 ) 2 (OH) 2 , is orthorhombic, Cccm , with unit-cell parameters derived from a crystal-structure refinement: a 16.461(2), b 7.434(1), c 12.131(2) A, V 1484.5(6) A 3 , a:b:c 2.2143:1:1.6318, Z = 8. The strongest nine lines of the X-ray powder-diffraction pattern [ d in A (I)( hkl )] are: 4.874(90)(202), 3.473(50)(113), 3.389(60)(220), 3.167(100)(022), 3.015(50)(510), 2.988(50)(313), 2.919(70)(511), 2.503(90)(422,314) and 1.775(50)(533,026). The mineral occurs within a vug 3 cm across on a single specimen of gangue collected from the 31 st level of the Tsumeb mine, Tsumeb, Namibia, as platy to compact anhedral to subhedral masses. These masses, up to 0.3 mm in maximum size, are intimately intergrown with very dark green to black botryoidal masses of an intergrowth of two tsumcorite-group minerals. Individual fragments are between 50 and 100 μm in size, with no obvious forms, and {100} and {011} as imperfect cleavages. Sewardite has physical properties that are very similar to those of carminite; it is dark red in masses to a much lighter red to orange on thin edges of small fragments. The streak is reddish brown, and the luster, vitreous. It is translucent (masses) to transparent (on thin edges), and nonfluorescent. The hardness (Mohs) is 3½. It is brittle, and has a splintery (in the [011] direction) to uneven fracture. The calculated density is 4.156 g/cm 3 (for the empirical formula). In polished section, it is light bluish grey in plane-polarized reflected light in air, with ubiquitous very bright pink to red internal reflections; the mineral is very weakly bireflectant, non-anisotropic, without pleochroism. Averaged results of eight electron-microprobe analyses yield CaO 11.77, ZnO 1.68, CuO 0.28, Fe 2 O 3 31.65, As 2 O 5 48.81, H 2 O [4.04], total [98.23] wt.%. The empirical formula is Ca 0.99 (Fe 3+ 1.87 Zn 0.10 Cu 0.02 ) ∑1.99 As 2.01 5+ O 8.00 [(OH) 1.88 (H 2 O) 0.12 ] ∑2.00 , on the basis of 10 anions. The infrared-absorption spectra show bands for structural (OH), (H 2 O), and arsenate. The mineral’s name honors Terry M. Seward, Professor of Geochemistry, ETH, Zurich, Switzerland, who collected the mineral specimen in 1982. The crystal structure has been refined to an R index of 6.1% for 451 observed reflections measured with Mo K α X-radiation. Chains of edge-and corner-sharing Fe 3+ Φ 6 octahedra (Φ: O, OH) extend along the b axis and are linked by (AsO 4 ) tetrahedra to form [Fe 3+ 2 (AsO 4 ) 2 (OH) 2 ] sheets parallel to {001}; these sheets link via [8]-coordinated Ca atoms. Sewardite is the Ca-dominant analogue of carminite, ideally Pb 2+ Fe 3+ (AsO 4 ) 2 (OH) 2 .

On the symmetry of tsumcorite group minerals based on the new species rappoldite and zincgartrellite

AbstractRappoldite, the Co-analogue of helmutwinklerite, and zincgartrellite, the Zn-dominant analogue of gartrellite, are two new members of the tsumcorite group. Both minerals are triclinic, their structures are closely related to the parent structure, i.e. the ‘tsumcorite type’ (C2/m, Z = 2). The lower symmetry is caused by two different crystal-chemical requirements. Order phenomena of the hydrogen bonds cause the ‘helmutwinklerite type’ (P1̄, Z= 4), ordering of Cu2+and Fe3+ is responsible for the ‘gartrellite type’ (P1̄, Z = 1).Rappoldite was found on samples from the Rappold mine near Schneeberg, Saxony, Germany. The new species forms red to red-brown prismatic and tabular crystals up to 1 mm long. Dcalc. = 5.28 g/cm3. 2Vz = 85(5)°, nx = 1.85 (calc.), ny = 1.87(2) and nz = 1.90(2); dispersion is distinct with r > v; orientation is Y ∼∥ [1̄ 20] and X ∼ ∥ c. The empirical formula derived from electron microprobe analyses is (Pb1.01Ca0.01)Σ1.02(Co0.99Ni0.62Zn0.35Fe0.02)Σ1.98[(AsO4)1.99(SO4)0.01]Σ2.00[(OH)0.02(H2O)1.98]Σ2.00 or Pb(Co,Ni)2(AsO4)2·2H2O. Single-crystal X-ray studies showed average C2/m symmetry. Weak superstructure reflections are responsible for triclinic symmetry and enlarged cell metrics (refined from powder data): a= 11.190(2)Å, b= 10.548(2)Å, c= 7.593(1)Å, α = 100.38(1)8, β = 109.59(2)8, γ = 98.96(1)8, V= 807.6 Å3, Z= 4. The superstructure results from the hydrogen-bond scheme, but faint streaks indicate some disorder. All investigated rappoldite crystals are twinned by reflection on (23̄0) which corresponds to the mirror plane of the average C2/m cell. Helmutwinklerite is isotypic with rappoldite and probably also with pure thometzekite; sulphatian thometzekite is monoclinic.Zincgartrellite forms green-yellow rosette-like aggregates on samples from the Tsumeb mine, Namibia. The Dcalc. = 5.30 g/cm3. 2Vx = 87(5)°, nx = 1.91(2), ny = 1.94 (calc.) and nz = 1.97(2). Electron-microprobe analyses and Mössbauer data yielded the empirical formula (Pb0.97Ca0.04)Σ1.01(Zn0.91Cu0.51Fe0.59Al0.03)Σ2.04[(AsO4)1.96(SO4)0.01]Σ1.97[(OH)0.81(H2O)1.31]Σ2.12 or Pb(Zn,Fe,Cu)2(AsO4)2(H2O,OH)2. The structural formula is Pb(ZnxFe1–x)(ZnxCu1–x)(AsO4)2(OH)1–x(H2O)1+xwith 0.4 < x < 0.8. Gartrellite is defined by x < 0.4. Helmutwinklerite has x near to 1 and is defined by a cell with fourfold volume. Single-crystal X-ray studies of zincgartrellite proved space group P1̄ caused by ordering of Fe3+ and Cu at one atomic site. Cell parameters (refined from powder data): a= 5.550(1)Å, b= 5.620(1)Å, c= 7.621(1)Å, α = 68.59(1), β = 69.17(1), γ = 69.51(1)°, V= 200.1 Å3, Z= 1.