Search

Yttriaite-(Y), ideally Y2O3, is a new mineral (IMA2010-039) from the alluvial deposits of the Bol’shaya Pol’ya River, Subpolar Urals, Russia. The new mineral occurs as isolated crystals, typically cubo-octahedra <6 μm in size, embedded in massive native tungsten. Associated minerals include: copper, zircon, osmium, gold, and pyrite. The main forms observed are {100} and {111}. Due to the crystal size, physical properties could not be determined; however, the properties of synthetic Y2O3are well known. Synthetic Y2O3crystals are colorless to white with a white streak; crystals are transparent with an adamantine luster, while massive Y2O3is typically translucent with an earthy luster. Synthetic Y2O3has a Vickers hardness of 653.91, which corresponds to 5.5 on the Mohs scale. Synthetic Y2O3crystals have good cleavage on {111}. Yttriaite-(Y) is isotropic; the refractive index measured at 587 nm on synthetic Y2O3is n = 1.931. The empirical chemical formula (mean of 4 electron microprobe analyses) calculated on the basis of 3 O is: Y1.98Dy0.01Yb0.01O3. Yttriaite-(Y) is cubic, space group Ia3̅, with parameters a = 10.6018(7) Å, V = 1191.62(7) Å3, and Z = 16. The five strongest lines in the powder X-ray diffraction pattern (measured on synthetic Y2O3using synchrotron radiation) are [dobsin Å (I) (hkl)]: 3.0646 (100) (222), 1.8746 (55) (440), 1.5984 (38) (622), 2.6537 (26) (400), and 4.3356 (14) (211). The mineral name is based on the common name for the chemical compound, yttria.

Kapundaite, ideally (Na,Ca)2Fe43+(PO4)4(OH)3∙5H2O, is a new mineral (IMA2009-047) from Toms phosphate quarry, Kapunda, South Australia, Australia. The new mineral occurs as cavernous aggregates of fibers up to several centimeters across, associated with leucophosphite, natrodufrenite, and meurigite-Na crystals and amorphous brown, black, and/or greenish coatings. Individual kapundaite crystals are very thin flattened fibers up to a few millimeters in length, but typically no more than a few micrometers in thickness. The main form observed is {100}; other forms in the [010] zone are present, but cannot be measured. Crystals of kapundaite are pale to golden yellow, transparent to translucent, have a yellow streak and silky luster, and are non-fluorescent. Mohs hardness is estimated to be about 3; no twinning or cleavage was observed. Kapundaite is biaxial (+), with indices of refraction α = 1.717(3), β = 1.737(3), and γ = 1.790(3). 2V could not be measured; 2Vcalcis 64.7°. The optical orientation is Z = b, Y ≈ c with weak pleochroism: X = nearly colorless, Y = light brown, Z = pale brown; absorption: Y > Z > X. No dispersion was observed. The empirical chemical formula (mean of seven electron microprobe analyses) calculated on the basis of 24 O is (Ca1.13Na0.95)Σ2.08(Fe3+3.83Mn0.03Al0.02Mg0.01)Σ3.89P3.92O16(OH)3·5H2.11O. Kapundaite is triclinic, space group P1, a = 6.317(5), b = 7.698(6), c = 9.768(7) Å, α = 105.53(1)°, β = 99.24(2)°, γ = 90.09(2)°, V = 451.2(6) Å3, and Z = 1. The five strongest lines in the powder X-ray diffraction pattern are [dobsin Å (I) (hkl)]: 9.338 (100) (001), 2.753 (64) (21̄1), 5.173 (52) (011), 2.417 (48) (2̄1̄3, 202, 01̄4), and 3.828 (45) (02̄1). The crystal structure was solved from single-crystal X-ray diffraction data using synchrotron radiation and refined to R1= 0.1382 on the basis of 816 unique reflections with Fo > 4σF. The structure of kapundaite is based on a unique corrugated octahedral-tetrahedral sheet, which is composed of two types of chains parallel to a. Kapundaite is structurally related to mélonjosephite. The mineral is named for the nearest town to the quarry.

A series of lanthanide fluoride nanoparticles were prepared with a simple colloidal approach at 75 °C. All the nanoparticles are highly water-dispersible with sizes in the range of 3−10 nm. The light lanthanide fluoride salts, LaF3, CeF3, and NdF3, have the same trigonal crystal structure as the corresponding bulk materials. However, for the fluoride salts of the heavy Dy, Ho, Er, and Yb, nonstoichiometric cubic structures of NaxLnyFzcomposition were identified. Particularly, the middle GdF3and EuF3nanoparticles have both trigonal and orthorhombic crystal phases instead of a single orthorhombic phase as for the corresponding bulk materials, which is attributed to kinetically formed products. Study of La3+-doped GdF3nanoparticles showed that 15% La3+doping is sufficient for GdF3nanoparticles to crystallize completely in the trigonal phase, i.e., the same as LaF3, which is dramatically different than 50% La3+doping for the bulk. Finally, on the basis of the thermodynamic cycle for the preparation of the doped materials, calculations carried out explain well the published experimental results for the bulk. However, this approach failed to explain the results of the nanoparticles. Evidence is provided that the formation of kinetic products is responsible.

The photostability of semiconductor PbSe nanocrystals (NCs) under different storage conditions and the photoluminescence of PbSe NC films on Si substrates under vacuum and under different atmospheres were investigated. The NCs show a small blue shift in both the emission and absorption spectra when stored in solution. This blue shift is accelerated when the particles are stored in room light compared to when the particles are stored in the dark, which indicates that photooxidation is an important process. The photooxidation process is accelerated by irradiating NC solutions with a 450 W xenon lamp. The photobleaching and appearance of a precipitate are attributed to ligand desorption followed by agglomeration. Reversible O2-induced luminescence quenching was observed on a PbSe NC film on Si substrates, which could be addressed by two mechanisms:? indirect quenching by alteration of PbSe charging and neutralization dynamics or quenching through direct interaction of O2with the exciton. To improve the photostability of PbSe NCs, PbSe/PbS core/shell NCs using (TOP)S (TOP trioctylphosphine) and TMS2S (TMS2bis(trimethylsilyl)) as sulfur sources were prepared. However, PbSe/PbS core/shell NCs did not show an increased stability in solution upon irradiation with a xenon lamp when compared with PbSe core NCs. Either the PbS shell is not able to confine the charge carriers or there is incomplete shell passivation with the PbSe core, and as a result these core/shell NCs have comparable stability.

Most carbon on Earth is bound within minerals, and increasing the uptake of atmospheric carbon dioxide into minerals may reduce the greenhouse gas content of the atmosphere. We document carbon disposal through the mineralization of mine tailings at Clinton Creek, Yukon Territory, and Cassiar, British Columbia. We confirm crystallographic binding of carbon in these tailings and quantify carbon dioxide uptake using quantitative phase analysis with the Rietveld method for X-ray powder diffraction data. Planar disorder in the structures of the kaolinite-serpentine group minerals makes Rietveld refinements of X-ray powder diffraction data for serpentinites problematic. Using structureless pattern fitting and with the addition of a known quantity of a well-crystallized material, the problem of structural disorder is overcome by considering the serpentine minerals as amorphous phases. We test the accuracy and precision of this refinement method using synthetic serpentine-rich mine tailings of known composition. Estimates of the abundance of hydrated magnesium carbonates in these tailings have a precision of approximately 5% relative for mineral species present in amounts greater than 10 wt%. Precise estimates of carbonate mineral content and crystallographically bound atmospheric CO2are made for samples of serpentine-rich tailings from Clinton Creek and Cassiar. Results for mine tailings are also compared to mineralogically similar samples from a carbonate playa at Atlin, British Columbia. The potential for decomposition of metastable hydrated magnesium carbonate phases to geologically stable magnesite may represent long-term stability of the products of mineral sequestration in mine tailings.

The influence of F substitution on the local structure of Al in the tetrahedral and octahedral sheets of synthetic Al-rich phlogopite samples with nominal gel compositions of K(Mg3-xAlx)[Al1+xSi3-xO10] (OH)y(F)2-ybetween 0.0 ≤ x ≤ 0.8 and 0.5 ≤ y ≤ 1.8, was studied by 27Al MAS, MQMAS, {1H/19F} → 27Al 2D CPMAS (HETCOR) and {1H/19F} 27Al REDOR solid-state NMR and by IR spectroscopy. Changes in intensity of the absorption bands in the OH-stretching region of the IR spectra clearly indicate the incorporation of octahedral Al. Signals from the different phases can be separated in the 27Al MQMAS NMR spectra by generation of an isotropic dimension in F1. The 27Al quadrupolar parameters of the four phases were estimated from 27Al MAS NMR spectra obtained at 104.26 and 208.42 MHz. The quadrupolar coupling constant and isotropic chemical shift increases with increasing Al content for the IVAl site in phlogopite. The VIAl site shows a clear increase of the asymmetry parameter and CQwith increasing F content. The estimated 27Al signal areas show the lowest amount of impurity phases at high OH contents and a stabilization of VIAl sites by hydroxyl groups. The {1H} → 27Al 2D CPMAS (HETCOR) NMR experiment at short contact times provides information about site neighborhoods of tetrahedral Al sites and Mg3OH as well as Mg2AlOH sites, whereas magnetization is only transferred to the octahedral Al sites from hydroxyl groups in Mg2AlOH sites. The {19F} → 27Al 2D CPMAS (HETCOR) NMR spectrum is dominated by IVAl sites coupled to the Mg3F complex in phlogopite. Resonances from Mg2AlF complexes are not observed. Finally, the {1H/19F} 27Al REDOR experiments support the results of the 2D CPMAS (HETCOR) experiments.

The influence of F content on the formation and stability of Al-rich phlogopite has been investigated. Samples with varying OH/F-ratios and nominal gel compositions of K(Mg3-xAlx)(Al1+xSi3-xO10)(OH)y (F)2-y(0.0 < x < 0.8 and 0.5 < y < 1.8) were studied using 29Si, 1H, and 19F MAS NMR spec­troscopies, powder X-ray diffraction, electron-probe microanalysis, and scanning electron mi­croscopy. The synthetic phlogopites were synthesized from sol-gels in cold-seal pressure vessels at 1073 K, 2 kbar. The main phase (phlogopite) and three other impurity phases [corundum (α-Al2O3), kalsilite (KAlSiO4), and potassium aluminum hexafluoride (K3AlF6-0.5H20)] were clearly identi­fied by powder X-ray diffraction and electron-probe microanalysis. For phlogopite, the unit-cell parameters a0and b0decrease whereas C0increases with increasing Al-content (x). The average crystal size of phlogopite is about 1-2 pm. The 29Si MAS NMR spectra show up to four resonances at approximately -91, -87, -83, and -80 ppm, which can be assigned as Q3(n Al) signals with n = 0 - 3. The ideal Si/ivAl ratio calculated from the initial composition is always lower than that derived experimentally. Hydroxyl-rich compositions indicate an increased Al-content in the tetrahedral sheets, suggesting a stabilizing effect on the formation of Al-rich phlogopite. These conclusions are sup­ported by 1H and 19F MAS NMR spectra. The 1H MAS NMR spectra show a water signal at 4.7 ppm, a signal due to Mg2AlOH at 1.8 ppm, and a signal due to Mg3OH at 0.7 ppm. The 19F MAS NMR spectra exhibit a signal for Mg2AlF at -150 ppm, one due to AlF6(K3AlF6-0.5H20) at -157 ppm, and one for Mg3F at -174 ppm. Comparison of the 1H and 19F MAS NMR spectra for different Al- and F- contents reveals a non-statistical distribution of F- and OH-groups at the crystallographic sites in the octahedral sheets where F prefers sites coordinated by three Mg, and OH sites with Al in the next- nearest coordination sphere.

Single-crystal structure-refinement and electron-microprobe analysis of synthetic amphiboles with nominal fluoro-eckermannite composition and different trivalent cations (Al, Sc, Ti3+, V3+, Cr3+, Ga,) show significant deviations from nominal stoichiometry. Synthetic Sc- and Cr-bearing fluoro-eckermannite are close to nominal stoichiometry, whereas the corresponding nominal Al-, V3+-, Ga-, and Ti-bearing species contain very few trivalent cations and approximate Na(NaMg)Mg5Si8O22F2, a composition that has not been found in natural systems. The presence of a significant cummingtonite component strongly affects unit-cell parameters, coordination geometry around the B-, C-, and T-group sites, and cation ordering at the A-group sites. The high-charge cations are completely ordered at the M2 site, and there is a well-developed linear relationship between and the constituent-cation radius at the M2 site. The synthetic fluoro-eckermannite structure is stabilized by large spherically symmetric trivalent cations at the M2 site; for small spherically symmetric trivalent cations, it is not stable (at least at the synthesis conditions used here). Synthetic chromium-fluoro-eckermannite is stabilized by the non-spherically symmetric 3d2electronic arrangement, whereas Ga and V3+(3d2) do not stabilize the fluoroeckermannite structure.

AbstractIndexed X-ray powder diffraction data and crystal data are reported for: synthetic pargasite (P: NaCa2Mg4AlSi6Al2O22(OH)2), fluor-pargasite (FP: NaCa2Mg4AlSi6Al2O22F2), scandian pargasite (SP: NaCa2Mg4.4Sc0.6Si6Al2O22(OH)2) and scandian fluor-pargasite (SFP: NaCa2Mg4.2Sc0.8Si6Al2O22F2).