ALBERT

Description: 〈span〉〈div〉Abstract〈/div〉Samples of the pharmacosiderite group were synthesized either directly, from aqueous solutions at 160 °C, or by ion exchange over extended periods of time at 100 °C. In more than 200 experiments, no pure pharmacosiderite sample was obtained, and a protocol was developed to remove scorodite and arsenical iron oxides from the samples. In this way, K-, Na-, Ba-, and Sr-dominant pharmacosiderite samples were prepared. The chemical compositions of the two samples used for further experiments were Ba〈sub〉0.702〈/sub〉Fe〈sub〉4〈/sub〉[(AsO〈sub〉4〈/sub〉)〈sub〉0.953〈/sub〉(SO〈sub〉4〈/sub〉)〈sub〉0.047〈/sub〉]〈sub〉3〈/sub〉(OH)〈sub〉3.455〈/sub〉O〈sub〉0.545〈/sub〉·5.647H〈sub〉2〈/sub〉O and K〈sub〉1.086〈/sub〉Fe〈sub〉4〈/sub〉[(AsO〈sub〉4〈/sub〉)〈sub〉0.953〈/sub〉(SO〈sub〉4〈/sub〉)〈sub〉0.047〈/sub〉]〈sub〉3〈/sub〉 (OH)〈sub〉3.772〈/sub〉O〈sub〉0.228〈/sub〉·4.432H〈sub〉2〈/sub〉O. The Ba-dominant pharmacosiderite is tetragonal at room temperature, and the K-dominant pharmacosiderite is cubic. Upon heating, both samples lose zeolitic H〈sub〉2〈/sub〉O (shown by thermogravimetry), and this loss is accompanied by unit-cell contraction. In Ba-dominant pharmacosiderite, this loss also seems to be responsible for a symmetry change from tetragonal to cubic. The slight unit-cell contraction in Ba-dominant pharmacosiderite at 〈100 °C might be attributed to either negative thermal expansion or minor H〈sub〉2〈/sub〉O loss; our data cannot differentiate between these two possibilities. Both samples persisted in a crystalline state up to 320 °C (the highest temperature of the powder XRD experiment), showing that pharmacosiderite is able to tolerate almost complete removal of the zeolitic H〈sub〉2〈/sub〉O molecules. Low-temperature heat capacity measurements show a diffuse magnetic anomaly for K-dominant pharmacosiderite at ≈5 K and a sharp lambda transition for Ba-dominant pharmacosiderite at 15.2 K. The calculated standard entropy at 〈span〉T〈/span〉 = 298.15 is 816.9 ± 5.7 J/molK for K-dominant pharmacosiderite (molecular mass 824.2076 g/mol, see formula above) and 814.1 ± 5.5 J/molK for Ba-dominant pharmacosiderite (899.7194 g/mol).〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉We have investigated a locality very well known to mineral collectors, the Yates U-Th prospect near Otter Lake, Québec. There, dikes of orange to pink calcite enclose euhedral prisms of fluorapatite, locally aligned. Early investigators pointed out the importance of micro-inclusions in the prisms. We describe and image the micro-inclusions in two polished sections of fluorapatite prisms, one of them with a millimetric globule of orange calcite similar to that in the matrix. We interpret the globule to have been an inclusion of melt trapped during growth. Micro-globules disseminated in the fluorapatite are interpreted to have crystallized 〈span〉in situ〈/span〉 from aliquots of the boundary-layer melt enriched in constituents rejected by the fluorapatite; the micro-globules contain a complex jigsawed assemblage of carbonate, silicate, and sulfate minerals. Early minerals to crystallize are commonly partly dissolved and partly replaced by lower-temperature phases. Such jigsawed assemblages seem to be absent in the carbonate matrix sampled away from the fluorapatite prisms. The pressure and temperature attained at the Rigolet stage of the Grenville collisional orogeny were conducive to the anatexis of marble in the presence of H〈sub〉2〈/sub〉O. The carbonate melt is considered to have become silicocarbonatitic by assimilation of the enclosing gneisses, which were also close to their melting point. Degassing was important, and the melt froze quickly. The evidence points to a magmatic origin for the carbonate dikes and the associated clinopyroxenite, rather than a skarn-related association.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The Lower Group chromitites of the Bushveld Igneous Complex are mined for chromite as a primary product. The recovery of platinum group elements and base metals (Ni, Cu) as by products has the potential to add value to the chromite resources. This study focuses on the LG-6 and LG-6A chromitite seams at the Thaba mine located on the western limb of the Bushveld Complex. Platinum group minerals and base-metal sulfides are studied by mineral liberation analysis and electron microprobe analysis to define distinct assemblages and to evaluate the potential for beneficiation. Based on the results, two distinct major mineral assemblages are defined. The first assemblage is rich in platinum group element-sulfides, along with variable proportions of malanite/cuprorhodsite and alloys of Fe and Sn. The associated base metal sulfides are dominated by chalcopyrite and pentlandite, along with pyrite and subordinate millerite/violarite. Associated silicates are mainly primary magmatic orthopyroxene and plagioclase. The second assemblage is rich in platinum group element-sulfarsenides and -arsenides as well as -antimonides and -bismuthides and is associated with a base metal sulfide assemblage dominated by pentlandite and Co-rich pentlandite. The second assemblage is also marked by an abundance of alteration minerals, such as talc, serpentine, and/or carbonates, which are closely associated with the platinum group minerals. Statistical evaluation reveals that the two mineral assemblages cannot be attributed to their derivation from different chromitite seams but document the effects of pervasive hydrothermal alteration. Alteration evidently had similar effects on the different chromitite seams. The occurrence and distribution of the two characteristic assemblages has important implications for beneficiation. Assemblages rich in platinum group element-sulfides associated with base metal sulfides respond well to flotation, unlike the alteration assemblages rich in arsenides, antimonides, and bismuthides. The nature of the gangue minerals will also impact platinum-group mineral recovery, as high phyllosilicate abundances, such as those encountered in the alteration assemblage, may cause problems during flotation and lead to poor recoveries.〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Jahnsite-(NaMnMg), (Na,Ca)(Mn〈sup〉2+〈/sup〉,Fe〈sup〉3+〈/sup〉)(Mg,Fe〈sup〉3+〈/sup〉,Mn〈sup〉3+〈/sup〉)〈sub〉2〈/sub〉Fe〈sup〉3+〈/sup〉〈sub〉2〈/sub〉(PO〈sub〉4〈/sub〉)〈sub〉4〈/sub〉(OH)〈sub〉2〈/sub〉(H〈sub〉2〈/sub〉O)〈sub〉8〈/sub〉, is a new mineral from the Sapucaia pegmatite, Conselheiro Pena pegmatite district, Minas Gerais, Brazil, and the White Rock No. 2 quarry, Bimbowrie Conservation Park, South Australia, Australia. At both localities, it is a low temperature, secondary mineral formed as the result of alteration of primary phosphates. The mineral occurs as light orange to orange-yellow prisms, elongate on [100], exhibiting the forms {100}, {001}, and {011} and twinned by reflection on {001}. The streak is white, the luster is vitreous, and crystals are transparent to translucent. The Mohs hardness is about 4. The tenacity is brittle, the fracture is irregular, stepped (splintery), and there is one very good cleavage on {001}. The measured density is 2.68(1) g/cm〈sup〉3〈/sup〉 (Sapucaia). The mineral is slowly soluble in dilute HCl. Jahnsite-(NaMnMg) from Sapucaia is biaxial (–), with α 1.642(1), β 1.675(1), γ 1.677(1) (white light). The measured 2〈span〉V〈/span〉 is 29(1)°. Dispersion is very strong, 〈span〉r〈/span〉 〈 〈span〉v〈/span〉. The optical orientation is 〈span〉Z〈/span〉 = 〈strong〉b〈/strong〉; 〈span〉X〈/span〉 ^ 〈strong〉c〈/strong〉 = 51° in obtuse β. Pleochroism is 〈span〉X〈/span〉 = colorless, 〈span〉Y〈/span〉 and 〈span〉Z〈/span〉 = orange-yellow; 〈span〉Y〈/span〉 ≈ 〈span〉Z〈/span〉 〉 〈span〉X〈/span〉. Electron-microprobe analyses gave the empirical formulae (Na〈sub〉0.56〈/sub〉Ca〈sub〉0.25〈/sub〉Mn〈sup〉2+〈/sup〉〈sub〉0.09〈/sub〉)〈sub〉Σ0.90〈/sub〉(Mn〈sup〉2+〈/sup〉〈sub〉0.85〈/sub〉Fe〈sup〉3+〈/sup〉〈sub〉0.15〈/sub〉)〈sub〉Σ1.00〈/sub〉(Mg〈sub〉1.53〈/sub〉Fe〈sup〉3+〈/sup〉〈sub〉0.47〈/sub〉)〈sub〉Σ2.00〈/sub〉(Fe〈sup〉3+〈/sup〉〈sub〉1.79〈/sub〉Al〈sub〉0.21〈/sub〉)〈sub〉Σ2〈/sub〉(PO〈sub〉4〈/sub〉)〈sub〉4〈/sub〉(OH)〈sub〉1.83〈/sub〉(H〈sub〉2〈/sub〉O)〈sub〉8.17〈/sub〉 for the Sapucaia material and (Na〈sub〉0.63〈/sub〉Ca〈sub〉0.23〈/sub〉Mn〈sup〉2+〈/sup〉〈sub〉0.14〈/sub〉)〈sub〉Σ1.00〈/sub〉(Mn〈sup〉2+〈/sup〉〈sub〉0.68〈/sub〉Mn〈sup〉3+〈/sup〉〈sub〉0.26〈/sub〉Fe〈sup〉3+〈/sup〉〈sub〉0.05〈/sub〉Mg〈sub〉0.01〈/sub〉)〈sub〉Σ1.00〈/sub〉(Mg〈sub〉1.26〈/sub〉Mn〈sup〉2+〈/sup〉〈sub〉0.43〈/sub〉Mn〈sup〉3+〈/sup〉〈sub〉0.16〈/sub〉Fe〈sup〉3+〈/sup〉〈sub〉0.15〈/sub〉)〈sub〉Σ2.00〈/sub〉(Fe〈sup〉3+〈/sup〉〈sub〉1.97〈/sub〉Al〈sub〉0.02〈/sub〉)〈sub〉Σ1.99〈/sub〉(PO〈sub〉4〈/sub〉)〈sub〉4〈/sub〉(OH)〈sub〉1.98〈/sub〉(H〈sub〉2〈/sub〉O)〈sub〉8.02〈/sub〉 for the White Rock material. The mineral is monoclinic, space group 〈span〉P〈/span〉2/〈span〉a〈/span〉, with cell parameters (Sapucaia) 〈span〉a〈/span〉 15.1045(15), 〈span〉b〈/span〉 7.1629(2), 〈span〉c〈/span〉 9.8949(7) Å, β 110.640(7)°, 〈span〉V〈/span〉 1001.83(13) Å〈sup〉3〈/sup〉, and 〈span〉Z〈/span〉 = 2. The structure refinements of crystals from both localities were generally consistent and showed the mineral to be a member of the jahnsite group (Sapucaia: 〈span〉R〈/span〉〈sub〉1〈/sub〉 = 3.19% for 1941 〈span〉I〈/span〉〈sub〉o〈/sub〉 〉 2σ〈span〉I〈/span〉 reflections; White Rock: 〈span〉R〈/span〉〈sub〉1〈/sub〉 = 6.94% for 13485 〈span〉I〈/span〉〈sub〉o〈/sub〉 〉 2σ〈span〉I〈/span〉 reflections).〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉The crystal structures of gem-quality richterite and pargasite from Afghanistan, space group 〈span〉C〈/span〉2/〈span〉m〈/span〉, 〈span〉Z〈/span〉 = 2, have been refined to 〈span〉R〈/span〉〈sub〉1〈/sub〉 indices of 2.47% and 3.22%, respectively, using Mo〈span〉K〈/span〉α X-radiation. Results from electron-microprobe analysis were used to calculate unit formulae and site populations were assigned using the refined site-scattering values and the observed mean bond-lengths. In pargasite, 〈sup〉[4]〈/sup〉Al is strongly ordered at 〈span〉T〈/span〉(1) and 〈sup〉[6]〈/sup〉Al is partly disordered over the 〈span〉M〈/span〉(2) and 〈span〉M〈/span〉(3) sites, whereas the 〈span〉M〈/span〉(1,2,3) sites are almost completely occupied by Mg in richterite. 〈sup〉A〈/sup〉Na is split between the 〈span〉A〈/span〉(2) and 〈span〉A〈/span〉(〈span〉m〈/span〉) sites and K occurs at the 〈span〉A〈/span〉(〈span〉m〈/span〉) site. The infrared spectra in the principal OH-stretching region were measured and the fine structure was fit to component bands that were assigned to short-range ion arrangements over the configuration symbol 〈span〉M〈/span〉(1)〈span〉M〈/span〉(1)〈span〉M〈/span〉(3)–O(3)–A–O(3):〈span〉T〈/span〉(1)〈span〉T〈/span〉(1), corresponding to the following local arrangements: MgMgMg–OH–Na–OH:SiSi; MgMgMg–OH–Na–F:SiSi; MgMgMg–OH–Na–F:SiAl; and MgMgMg–OH–□–OH:SiSi in richterite and MgMgMg–OH–Na–OH:SiAl; MgMgMg–OH–Na–F:SiAl; MgMgAl–OH–Na–OH:SiAl; and MgMgAl–OH–Na–F:SiAl in pargasite (□ = vacancy).〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Tamboite (〈span〉x〈/span〉 = 3; 〈span〉y〈/span〉 = 2) and metatamboite (〈span〉x〈/span〉 = 3; 〈span〉y〈/span〉 = 0), Fe〈sup〉3+〈/sup〉〈sub〉3〈/sub〉(SO〈sub〉4〈/sub〉)(Te〈sup〉4+〈/sup〉O〈sub〉3〈/sub〉)〈sub〉3〈/sub〉(Te〈sup〉4+〈/sup〉O(OH)〈sub〉2〈/sub〉)(OH)(H〈sub〉2〈/sub〉O)〈span〉x〈/span〉{H〈sub〉2〈/sub〉O}〈span〉y〈/span〉, are new tellurite minerals from the Tambo mine, Coquimbo Province, Chile. The two minerals transform to each other reversibly with changes in ambient humidity. They occur as pale-yellow clusters of radiating fiber bundles on the surface of a compact aggregate of silicified tuff. Tamboite and metatamboite are optically biaxial, and their calculated mean index of refraction is greater than 1.80. The calculated densities are 3.648 g/cm〈sup〉3〈/sup〉 for tamboite and 4.053 g/cm〈sup〉3〈/sup〉 for metatamboite. Tamboite and metatamboite are monoclinic, space group 〈span〉P〈/span〉2〈sub〉1〈/sub〉/〈span〉c〈/span〉, 〈span〉Z〈/span〉 = 4. Unit-cell parameters for tamboite are 〈span〉a〈/span〉 16.879(10), 〈span〉b〈/span〉 7.310(4), 〈span〉c〈/span〉 16.666(9) Å, β 108.857(11)°, 〈span〉V〈/span〉 1958(3) Å〈sup〉3〈/sup〉; for metatamboite they are 〈span〉a〈/span〉 14.395(5), 〈span〉b〈/span〉 7.296(4), 〈span〉c〈/span〉 16.411(6) Å, β 98.909(10)°, 〈span〉V〈/span〉 1703(2) Å〈sup〉3〈/sup〉. Chemical analysis by electron microprobe gave the empirical cations [calculated on the basis of 22 anions 〈span〉pfu〈/span〉 with OH = 3 and H〈sub〉2〈/sub〉O = 5 〈span〉pfu〈/span〉 (tamboite) or H〈sub〉2〈/sub〉O = 3 〈span〉pfu〈/span〉 (metatamboite)] as (Fe〈sup〉3+〈/sup〉〈sub〉3.10〈/sub〉Al〈sub〉0.15〈/sub〉)〈sub〉Σ3.25〈/sub〉(S〈sup〉6+〈/sup〉〈sub〉0.75〈/sub〉Se〈sup〉6+〈/sup〉〈sub〉0.05〈/sub〉)〈sub〉Σ0.80〈/sub〉Te〈sup〉4+〈/sup〉〈sub〉4.11〈/sub〉. The seven strongest lines in the X-ray powder diffraction patterns [listed as 〈span〉d〈/span〉 (Å), 〈span〉I〈/span〉, (〈span〉hkl〈/span〉)] are as follows: metatamboite: 14.221, 100, (100); 2.874, 13, ; 3.140, 12, (221); 3.423, 11, ; 3.400, 11, (312); 3.012, 11, ; 4.054, 9, ; tamboite: 16.068, 100, (100); 3.425, 9, ; 2.999, 8, ; 3.171, 6, (221); 2.853, 5, ; 4.153, 4, ; 3.943, 4, (004). The crystal structures were solved by direct methods and refined to 〈span〉R〈/span〉〈sub〉1〈/sub〉 indices of 4.3 and 3.0%. The structures consist of virtually identical ferric-sulfate-tellurite-hydrate slabs that are constructed from strands of ferric-sulfate-hydrate polyhedra linked by Te〈sup〉4+〈/sup〉 cations. In metatamboite, the slabs are linked directly by hydrogen bonds whereas in tamboite, interslab linkage occurs by hydrogen bonds through interstitial {H〈sub〉2〈/sub〉O}〈sub〉4〈/sub〉 clusters known as 〈span〉Ci〈/span〉 cyclic tetramers. Exposure of a crystal to a desiccant at room temperature resulted in a third variant (〈span〉x〈/span〉 = 2; 〈span〉y〈/span〉 = 0) with the structural formula Fe〈sup〉3+〈/sup〉〈sub〉2〈/sub〉Fe〈sup〉2+〈/sup〉(SO〈sub〉3〈/sub〉(OH))(Te〈sup〉4+〈/sup〉O〈sub〉3〈/sub〉)〈sub〉3〈/sub〉(Te〈sup〉4+〈/sup〉O(OH)〈sub〉2〈/sub〉)(OH)(H〈sub〉2〈/sub〉O)〈span〉x〈/span〉, space group 〈span〉P〈/span〉2〈sub〉1〈/sub〉/〈span〉c〈/span〉, 〈span〉Z〈/span〉 = 4, 〈span〉a〈/span〉 16.879(10), 〈span〉b〈/span〉 7.310(4), 〈span〉c〈/span〉 16.666(9) Å, β 108.857(11)°, 〈span〉V〈/span〉 1958(3) Å〈sup〉3〈/sup〉, calculated density 4.176 g/cm〈sup〉3〈/sup〉. This lower-hydrate variant has less cation-bonded (H〈sub〉2〈/sub〉O) than metatamboite and tamboite, and the ferric-sulfate-tellurite-hydrate slabs are polymerized to form a framework structure. Attempts to transform the lower hydrate back to tamboite or metatamboite at room temperature and elevated humidity were unsuccessful.〈/span〉

Description: 〈span〉rare-element-pegmatiteanatexisOxford County pegmatite fieldMaine〈/span〉

Description: 〈span〉〈div〉Abstract〈/div〉Samples of the pharmacosiderite group were synthesized either directly, from aqueous solutions at 160 °C, or by ion exchange over extended periods of time at 100 °C. In more than 200 experiments, no pure pharmacosiderite sample was obtained, and a protocol was developed to remove scorodite and arsenical iron oxides from the samples. In this way, K-, Na-, Ba-, and Sr-dominant pharmacosiderite samples were prepared. The chemical compositions of the two samples used for further experiments were Ba〈sub〉0.702〈/sub〉Fe〈sub〉4〈/sub〉[(AsO〈sub〉4〈/sub〉)〈sub〉0.953〈/sub〉(SO〈sub〉4〈/sub〉)〈sub〉0.047〈/sub〉]〈sub〉3〈/sub〉(OH)〈sub〉3.455〈/sub〉O〈sub〉0.545〈/sub〉·5.647H〈sub〉2〈/sub〉O and K〈sub〉1.086〈/sub〉Fe〈sub〉4〈/sub〉[(AsO〈sub〉4〈/sub〉)〈sub〉0.953〈/sub〉(SO〈sub〉4〈/sub〉)〈sub〉0.047〈/sub〉]〈sub〉3〈/sub〉 (OH)〈sub〉3.772〈/sub〉O〈sub〉0.228〈/sub〉·4.432H〈sub〉2〈/sub〉O. The Ba-dominant pharmacosiderite is tetragonal at room temperature, and the K-dominant pharmacosiderite is cubic. Upon heating, both samples lose zeolitic H〈sub〉2〈/sub〉O (shown by thermogravimetry), and this loss is accompanied by unit-cell contraction. In Ba-dominant pharmacosiderite, this loss also seems to be responsible for a symmetry change from tetragonal to cubic. The slight unit-cell contraction in Ba-dominant pharmacosiderite at 〈100 °C might be attributed to either negative thermal expansion or minor H〈sub〉2〈/sub〉O loss; our data cannot differentiate between these two possibilities. Both samples persisted in a crystalline state up to 320 °C (the highest temperature of the powder XRD experiment), showing that pharmacosiderite is able to tolerate almost complete removal of the zeolitic H〈sub〉2〈/sub〉O molecules. Low-temperature heat capacity measurements show a diffuse magnetic anomaly for K-dominant pharmacosiderite at ≈5 K and a sharp lambda transition for Ba-dominant pharmacosiderite at 15.2 K. The calculated standard entropy at 〈span〉T〈/span〉 = 298.15 is 816.9 ± 5.7 J/molK for K-dominant pharmacosiderite (molecular mass 824.2076 g/mol, see formula above) and 814.1 ± 5.5 J/molK for Ba-dominant pharmacosiderite (899.7194 g/mol).〈/span〉

Description: 〈span〉lithiumpegmatiteremote sensingexplorationFregeneda-AlmendraPortugalSpain〈/span〉

Description: 〈span〉tourmalinetitaniumsubstitutionspegmatiteexocontact〈/span〉