ALBERT

Description: Phosphoran olivine (1–7 wt% P 2 O 5 ) is a metastable phase known from fewer than a dozen meteoritic or terrestrial occurrences. We have thoroughly examined phosphoran olivine in the Springwater pallasite to characterize its distribution, textural relationships, and geochemistry. Phosphoran olivine is abundant in Springwater as randomly distributed millimeter-scale partial overgrowths on the P-free olivine crystals. Geochemical analyses support the substitution mechanism of P into the tetrahedral Si site with octahedral site vacancies for charge balance; observed trace element variations, on the other hand, are not related to P substitution. Element mapping reveals fine-scale oscillatory P zoning in unusual serrate patterns, indicating rapid crystal nucleation from a melt as proposed by Boesenberg and Hewins (2010) and a subsequently variable rate of crystallization. The timing of phosphoran olivine formation in Springwater is constrained to after the period of macroscopic olivine rounding but before the cooling of the metal matrix; because the phosphoran overgrowths overprint specific host grain boundary modifications, we suggest that the episode of extremely rapid cooling necessary to crystallize and preserve this rare phase may have been triggered by an additional impact to the parent body.

Description: The crystal structures of seven members of the graftonite-beusite series, ideally (Fe 2+ ,Mn 2+ ,Ca) 3 (PO 4 ) 2 , monoclinic P 2 1 / c, a 8.77–8.81, b 11.43–11.58, c 6.13–6.17 Å, β 99.19–99.32°, V 607.5–617.7 Å 3 , have been refined to R 1 indices of 2.1–3.7% using ~1300–1600 unique observed reflections (| F o | 〉 5 F ) collected using a single-crystal diffractometer equipped with Mo K α X-radiation. The crystals used in the collection of the X-ray data were subsequently analyzed with an electron microprobe and the structural and microprobe results were used to assign site populations. The refined site-scattering values and linear variation in mean bond-length as a function of aggregate-cation radius indicate that Ca is completely ordered at the M (1) site. Similarly Mn is ordered at the M (1) and M (3) sites, with any excess Mn occurring at M (2), and Mg is completely ordered at M (2). Detailed consideration of incident bond-valence sums at the three M sites indicates that the coordination numbers of the M (1), M (2), and M (3) sites are [8], [5], and [6], respectively, although the differences between these and [7], [5], and [5] are very small. Ca is dominant at the M (1) site in a previously refined beusite structure, and there are compositions reported here and elsewhere in which Ca is dominant at M (1) in graftonite-like compositions, indicating the potential for new mineral species in this group.

Description: 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 a = 1.671, ß = 1.687, ? = 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 P1I, with a = 5.9756(4), b = 7.6002(5), c = 5.4471(4) Å, a = 84.2892(9), ß = 90.4920(9), ? = 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, 1I10); 7.526, 71, (010); 2.974, 49, (200, 022I); 3.253, 40, (021, 120); 2.701, 39, (2I10, 002, 1I2I1); 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)S2.92As2.03O8(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 (MoKa 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.

Description: 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 a = 1.671, ß = 1.687, ? = 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 P1I, with a = 5.9756(4), b = 7.6002(5), c = 5.4471(4) Å, a = 84.2892(9), ß = 90.4920(9), ? = 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, 1I10); 7.526, 71, (010); 2.974, 49, (200, 022I); 3.253, 40, (021, 120); 2.701, 39, (2I10, 002, 1I2I1); 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)S2.92As2.03O8(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 (MoKa 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.

Description: 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, (2İ02); 3.744, 11, (300); 2.655, 9, (230); 1.598, 8, (1İ52); 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 R1 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.

Description: 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 a = 1.671, ß = 1.687, ? = 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 P1I, with a = 5.9756(4), b = 7.6002(5), c = 5.4471(4) Å, a = 84.2892(9), ß = 90.4920(9), ? = 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, 1I10); 7.526, 71, (010); 2.974, 49, (200, 022I); 3.253, 40, (021, 120); 2.701, 39, (2I10, 002, 1I2I1); 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)S2.92As2.03O8(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 (MoKa 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.

Description: Borate minerals composed of [B 3 ] triangles and/or [B 4 ] tetrahedra ( = O or OH) commonly exhibit complex polymerizations to form diverse polyanion groups. High-resolution solid-state magic angle spinning (MAS) 11 B and 25 Mg NMR spectroscopy at moderate to ultrahigh magnetic fields (9.4, 14.1, and 21.1 T) allows for very accurate NMR parameters to be obtained for the borate dimorphs, inderite, and kurnakovite, [MgB 3 O 3 (OH) 5 ·5H 2 O]. Improved agreement between experimental results and ab initio density functional theory (DFT) calculations using Full Potential Linear Augmented Plane Wave (FP LAPW) with WIEN2k validates the geometry optimization procedures for these minerals and permits refinements of the hydrogen positions relative to previous X-ray diffraction crystal structures. In particular, the optimized structures lead to significant improvements in the positions of the H atoms, suggesting that H atoms have significant effects on the 11 B and 25 Mg NMR parameters in inderite and kurnakovite. This study shows that combined high-resolution NMR spectroscopy and ab initio theoretical modeling provides an alternative method for the refinement of crystal structures, especially H positions.

Description: The crystal structure of legrandite -- Zn 2 (AsO 4 )(OH)(H 2 O), monoclinic, a 12.8052(3), b 7.9249(2), c 10.2173(2) Å, β 104.4329(3)°, V 1004.13(6) Å 3 , space group P 2 1 / c , Z = 2 -- has been refined to an R 1 value of 1.2% based on 2844 unique [| F o | 〉 4 F ] reflections measured with a Bruker D8 three-circle diffractometer equipped with a rotating-anode generator (Mo K α X-radiation), multilayer optics, and an APEX-II detector. The legrandite structure is a heteropolyhedral framework of (AsO 4 ) tetrahedra, (Zn 5 ) square pyramids, and (Zn 6 ) octahedra [ = O, (OH), (H 2 O)] with extensive hydrogen bonding across its interstices. All hydrogen positions were located, all hydrogen bonds were assigned, and the H...O distances are in reasonable accord with the published relation between O–H stretching frequency and H...O bond-length.