No abstract

AbstractThe composition, structure, X-ray powder diffraction pattern, optical properties, density, infrared, Raman and Mössbauer spectra, and thermal properties of a homogeneous sample of metavivianite from the Boa Vista pegmatite, near Galiléia, Minas Gerais, Brazil are reported for the first time. Metavivianite is biaxial (+) with α = 1.600(3), β = 1.640(3), γ = 1.685(3) and 2Vmeas= 85(5)°. The measured and calculated densities are Dmeas= 2.56(2) and Dcalc= 2.579 g cm–3. The chemical composition, based on electronmicroprobe analyses, Mössbauer spectroscopy (to determine the Fe2+:Fe3+ratio) and gas chromatography (to determine H2O) is MgO 0.70, MnO 0.92, FeO 17.98, Fe2O326.60, P2O528.62, H2O 26.5; total 101.32 wt.%. The empirical formula is (Fe3+1.64Fe2+1.23Mg0.085Mn0.06)Σ3.015(PO4)1.98(OH)1.72·6.36H2O. Metavivianite is triclinic, P1̄, a = 7.989(1), b = 9.321(2), c = 4.629(1) Å, α = 97.34(1), β = 95.96(1), γ = 108.59(2)°, V = 320.18(11) Å3and Z = 1. The crystal structure was solved using a single-crystal techniques to an agreement index R = 6.0%. The dominant cations in the independent sites are Fe2+and Fe3+, with multiplicities of 1 and 2, respectively. The simplified crystal-chemical formula for metavivianite is Fe2+(Fe3+, Fe2+)2(PO4)2(OH,H2O)2·6H2O; the endmember formula is Fe2+Fe3+2(PO4)2(OH)2·6H2O, which is dimorphous with ferrostrunzite.

Kyanoxalite, a new member of the cancrinite group, has been identified in hydrothermally altered hyperalkaline rocks and pegmatites of the Lovozero alkaline pluton, Kola Peninsula, Russia. It was found at Mount Karnasurt (holotype) in association with nepheline, aegirine, sodalite, nosean, albite, lomonosovite, murmanite, fluorapatite, loparite, and natrolite and at Mt. Alluaiv. Kyanoxalite is transparent, ranging in color from bright light blue, greenish light blue and grayish light blue to colorless. The new mineral is brittle, with a perfect cleavage parallel to (100). Mohs hardness is 5-5.5. The measured and calculated densitiesare 2.30(1) and 2.327 g/cm 3 , respectively. Kyanoxalite is uniaxial, negative, ω = 1.794(1), ε = 1.491(1). It is ple ochroic from colorless along E to light blue along O. The IR spectrum indicates the presence of oxalate anions C 2 and water molecules in the absence of C Oxalate ions are confirmed by anion chromatography. The chemical composition (electron microprobe; water was determined by a modified Penfield method and carbon was determined by selective sorption from annealing products) is as follows, wt %: 19.) 0.13 (PO 4 ) 0.09 (OH) 0.01 ] Σ0.68 ⋅ 4.74H 2 O. The idealized formula is Na 7 (Al 5-6 Si 6-7 O 24 )(C 2 O 4 ) 0.5-1 ⋅ 5H 2 O. Kyanoxalite is hexagonal, the space group is P6 3 , a = 12.744(8), c = 5.213(6) Å. The strongest reflections in the X ray powder diffraction pattern are as follows, [d, [A] (I, %)(hkl). According to the X ray single crystal study (R = 0.033), two independent C 2 O 4 groups statistically occupy the sites on the axis 6 3 . The new mineral is the first natural silicate with an additional organic anion and is the most hydrated member of the cancrinite group. Its name reflects the color (κεανος is light blue in Greek) and the species forming role of oxalate anions. The holotype is deposited at the Fersman Mineralogical Museum of the Russian Academy of Sci ences, Moscow, registration no. 3735/1.

No abstract

No abstract

Hydronium (oxonium) cation H3O+ plays an important role in mineralogy and mineral structures. However, it is rather difficult to detect it using conventional methods of crystal structure analysis. In particular, hydronium‐bearing eudialyte‐group minerals (EGMs) are well known. In this paper, we provide data on a low‐temperature X‐ray structure analysis and vibrationl spectroscopy study of previously described “potassium‐oxonium eudialyte” from the Khibiny alkaline massif (Kola Peninsula, Russia) as well as new data on vibrational spectra and hydrogen bonding of a series of sodium‐deficient hydrated EGMs including new samples and minerals whose crystal structures were investigated earlier. Based on single‐crystal X‐ray structural analysis and Raman spectroscopy, it is shown that natural sodium‐deficient hydrated zirconosilicates related to eudialyte contain different hydrated proton complexes with extremely strong hydrogen bonds. The data obtained have been compared with recent high‐level quantum electronic and vibrational calculations. Some hydrated proton complexes in hydrated eudialyte‐related minerals have Zundel‐ and Eigen‐type configurations with the O˙˙˙O distances of ~2.40 and ~2.55 Å, respectively.

No abstract

No abstract