Polytypism in mcalpineite: a study of natural and synthetic Cu3TeO6

Synthetic and naturally occurring forms of tricopper orthotellurate, Cu^II₃Te^VIO₆ (the mineral mcalpineite) have been investigated by 3D electron diffraction (3D ED), X-ray powder diffraction (XRPD), Raman and infrared (IR) spectroscopic measurements. As a result of the diffraction analyses, Cu^II₃Te^VIO₆ is shown to occur in two polytypes. The higher-symmetric Cu^II₃Te^VIO₆-1C polytype is cubic, space group Ia3, with a = 9.537 (1) Å and V = 867.4 (3) ų as reported in previous studies. The 1C polytype is a well characterized structure consisting of alternating layers of Cu^IIO₆ octahedra and both Cu^IIO₆ and Te^VIO₆ octahedra in a patchwork arrangement. The structure of the lower-symmetric orthorhombic Cu^II₃Te^VIO₆-2O polytype was determined for the first time in this study by 3D ED and verified by Rietveld refinement. The 2O polytype crystallizes in space group Pcca, with a = 9.745 (3) Å, b = 9.749 (2) Å, c = 9.771 (2) Å and V = 928.3 (4) ų. High-precision XRPD data were also collected on Cu^II₃Te^VIO₆-2O to verify the lower-symmetric structure by performing a Rietveld refinement. The resultant structure is identical to that determined by 3D ED, with unit-cell parameters a = 9.56157 (19) Å, b = 9.55853 (11) Å, c = 9.62891 (15) Å and V = 880.03 (2) ų. The lower symmetry of the 2O polytype is a consequence of a different cation ordering arrangement, which involves the movement of every second Cu^IIO₆ and Te^VIO₆ octahedral layer by (1/4, 1/4, 0), leading to an offset of Te^VIO₆ and Cu^IIO₆ octahedra in every second layer giving an ABAB* stacking arrangement. Syntheses of Cu^II₃Te^VIO₆ showed that low-temperature (473 K) hydrothermal conditions generally produce the 2O polytype. XRPD measurements in combination with Raman spectroscopic analysis showed that most natural mcalpineite is the orthorhombic 2O polytype. Both XRPD and Raman spectroscopy measurements may be used to differentiate between the two polytypes of Cu^II₃Te^VIO₆. In Raman spectroscopy, Cu^II₃Te^VIO₆-1C has a single strong band around 730 cm^-1, whereas Cu^II₃Te^VIO₆-2O shows a broad double maximum with bands centred around 692 and 742 cm^-1.

Lumsdenite, NaCa3Mg2(As3+V4+2V5+10As5+6O51)·45H2O, a new polyoxometalate mineral from the Packrat mine, Mesa County, Colorado, USA

Lumsdenite (IMA 2018–092), ideally NaCa3Mg2(As3+V4+2V5+10As5+6O51)·45H2O, is a rare new polyoxometalate mineral from the Packrat mine, Gateway district, Mesa County, Colorado, USA. Crystals of lumsdenite occur as blades up to 0.2 mm in length, commonly growing in sprays. The crystals are dark green blue, with a green-blue streak. The mineral occurs on asphaltum, associated with montroseite- and corvusite-bearing sandstone. Other secondary minerals found in close association with lumsdenite are gypsum, huemulite, rösslerite, and at least two other potentially new minerals. Lumsdenite is optically biaxial (–), with α 1.617(2), β 1.651(5), and γ 1.675(5) in white light. The pleochroism scheme for lumsdenite is X = greenish yellow, Y = dark greenish blue, Z = greenish blue; X << Z < Y. The mineral is triclinic, , with a 10.3490(5), b 17.6263(9), c 23.2556(16) Å, α 82.208(6), β 88.351(6), γ 81.702(6)°, V 4158.8(4) Å3, and Z = 2. The strongest four powder diffraction lines for lumsdenite are [dobs Å(I)(hkl)]: , 14.86(80)(011), 17.30(44)(010), and 10.22(32)(100). The atomic arrangement of lumsdenite contains the novel polyoxometalate heteropolyanion [As3+V4+,5+12As5+6O51] structural unit in lumsdenite, [As3+V4+25+10As5+6O51]11−, which has previously been found in four other minerals from the Packrat mine. The charge of the structural unit is balanced by the charge of the [NaCa3Mg2(H2O)31·14H2O]11+ interstitial complex. The name lumsdenite is for the location of the mine at the head of Lumsden Canyon.

Okieite, Mg3[V10O28]·28H2O, a new decavanadate mineral from the Burro mine, Slick Rock mining district, San Miguel County, Colorado, USA

Okieite, Mg3[V10O28]·28H2O, is a new decavanadate mineral from the Burro mine, Slick Rock district, San Miguel County, Colorado, USA (type locality); the mineral is also found at the Hummer mine, Paradox Valley, Montrose County, also in Colorado. The mineral is rare; it occurs with dickthomssenite on montroseite- and corvusite-bearing sandstone. Crystals of okieite from the Burro mine are equant to prismatic, commonly appearing like curving columns (up to about 3 mm in length) and often exhibiting rounded faces. The streak of okieite is light orange yellow, and the luster is vitreous. The Mohs hardness is ca. 1½, the tenacity is brittle, the fracture is curved or conchoidal, there is no cleavage, and the measured density is 2.20(2) g/cm3. Okieite is biaxial (–), with α = 1.720(3), β = 1.745(3), γ = 1.765(3) (white light); 2V = 84(2)° with strong r < v dispersion. The optical orientation is X ^ a = 37°, Y ^ c = 28°, Z ^ b = 31°. No pleochroism is observed in okieite. The empirical formula from electron-probe microanalysis (calculated on the basis of V = 10 and O = 56 apfu as indicated by the structure) is Mg2.86[H0.28V5+10O28]·28H2O. Okieite is triclinic, , with a 10.55660(19), b 10.7566(2), c 21.3555(15)Å, α 90.015(6), β 97.795(7), γ 104.337(7)°, and V 2326.30(19)Å3, as determined by single-crystal X-ray diffractometry. The strongest four diffraction lines in the powder diffractograms are [d in Å(I)(hkl)]: 9.71(100); 8.32(19); 11.04(17)(002); and 6.42(12)(110, . The atomic arrangement of okieite [R1 = 0.0352 for 11,327 I > 2σI reflections] consists of a {V10O28}6– (decavanadate) structural unit and a {[Mg(H2O)6]3·10H2O}6+ interstitial complex. Only hydrogen bonding links the structural unit with the components of the interstitial complex. Okieite is isostructural with synthetic Mg3[V10O28]·28H2O. The name okieite is for Craig (“Okie”) Howell of Naturita, Colorado.

Cadwaladerite, Al2(H2O)(OH)4·n(Cl,OH–,H2O), from Cerros Pintados, Chile, defined as a valid mineral species and the discreditation of lesukite

Cadwaladerite, described in 1941 as Al(OH)2Cl·4H2O, and lesukite, described in 1997 as Al2(OH)5Cl·2H2O, are very closely related chemically and structurally, but are found in very different environments. Cadwaladerite was found at the edge of a salar in Chile. Lesukite has been described from a volcanic fumarole and from burning coal seams. Both materials have cubic symmetry with a = 19.788 to 19.859Å. The crystal structure, common to both, consists of a rigid three-dimensional framework of edge- and corner-sharing Al(OH,H2O)6 octahedra that contains large interconnected cavities where loosely held Cl, OH, and H2O are located. The fact that Cl is loosely held within the structure is demonstrated by a dramatic reduction in Cl content after washing the material in distilled water, while the structural integrity is maintained. Herein, cadwaladerite is confirmed as a valid mineral species and lesukite is discredited because the only difference between the two materials is the loosely held extra-framework Cl, OH, and H2O. Cadwaladerite, Al2(H2O)(OH)4·n(Cl,OH,H2O) (Z = 48) takes precedence over lesukite based on the date of description. Material similar to cadwaladerite is found as a corrosion product on some types of nuclear fuel elements and is also closely related to the molecular species used in antiperspirant and water filtration.

Nollmotzite, Mg[UV(UVIO2)2O4F3]·4H2O, the first natural uranium oxide containing fluorine

Nollmotzite (IMA2017-100), Mg[UV(UVIO2)2F3O4](H2O)4, is a new uranium oxide fluoride mineral found in the Clara mine, Black Forest Mountains, Germany. Electron microprobe analysis provided the empirical formula (Mg1.06Cu0.02)Σ1.08[UV(UVIO2)2O3.85F3.15][(H2O)3.69(OH)0.31]Σ4.00 based on three U and 15 O + F atoms per formula unit. Nollmotzite is monoclinic, space group Cm, with a = 7.1015 (12) Å, b = 11.7489 (17) Å, c = 8.1954 (14) Å, β = 98.087 (14)°, V = 676.98 (19) Å3 and Z = 2. The crystal structure [twinned by reticular merohedry; refined to R = 0.0369 with GoF = 1.09 for 1527 unique observed reflections, I > 3σ(I)] is based upon [UV(UVIO2)2F3O4]2- sheets of β-U3O8 topology and contains an interlayer with MgF2(H2O)4 octahedra. Adjacent sheets are linked through F-Mg-F bonds, as well as via hydrogen bonds. The presence of fluorine and pentavalent uranium in the structure of nollmotzite has potentially important implications for the safe disposal of nuclear waste.

The Impact of Bacterial Strain on the Products of Dissimilatory Iron Reduction

Three bacterial strains from the genus Shewanella were used to examine the influence of specific bacteria on the products of dissimilatory iron reduction. Strains CN32, MR-4 and W3-18-1 were incubated with HFO (hydrous ferric oxide) as the terminal electron acceptor and lactate as the organic carbon and energy source. Mineral products of iron reduction were analyzed using X-ray powder diffraction, electron microscopy, coulometry and susceptometry. Under identical nutrient loadings, iron reduction rates for strains CN32 and W3-18-1 were similar, and about twice as fast as MR-4. Qualitative and quantitative assessment of mineralized end products (secondary minerals) indicated that different products were formed during experiments with similar reduction rates but different strains (CN32 and W3-18-1), and similar products were formed during experiments with different iron reduction rates and different strains (CN32 and MR-4). The major product of iron reduction by strains CN32 and MR-4 was magnetite, while for W3-18-1 it was a mixture of magnetite and iron carbonate hydroxide hydrate (green rust), a precursor to fougerite. Another notable difference was that strains CN32 and MR-4 converted all of the starting ferric iron material into magnetite, while W3-18-1 did not convert most of the Fe(3+) into a recognizable crystalline material. Biofilm formation is more robust in W3-18-1 than in the other two strains used in this study. The differences in mineralization may be an indicator that EPS (or another cellular product from W3-18-1) may interfere with the crystallization of magnetite or facilitate formation of green rust. These results suggest that the relative abundance of mineral end products and the relative distribution of these products are strongly dependent on the bacterial species or strain catalyzing iron reduction.