Search

Since long time Raman scattering revealed to be a very sensitive and easy technique to deal with the detection of mineral compounds, due to their vibrational fingerprint. However, presence of small inclusions or identification of grains with very small dimensions in rocks may still remain problematic for normal Raman detection apparatus. In this work, we propose to apply the SERS (surface-enhancement Raman scattering) effect to micro-Raman measurements for the identification and characterization of pyroxene grains embedded in polymorphous rock matrices.

The crystal structure of the mineral routhierite, Tl(Cu,Ag)(Hg,Zn)(2)(As,Sb)(2)S(6), was solved and refined for the first time by means of single-crystal X-ray diffraction. The crystal structure consists of (Cu,Ag)S(4) and (Hg,Zn)S(4) tetrahedra, which share corners to form a framework with channels parallel to [001]. These channels contain TlS(6) and (As,Sb)S(3) polyhedra that share corners and edges with the tetrahedra. The crystal-chemical relationships with other Tl-Hg sulfosalts are outlined. The structure determination reported in this study definitively confirms that routhierite and stalderite possess the same crystal structure.

A review of the data available on the composition and abundance of titanium-bearing phases in the Earth's mantle is provided in the paper. The main attention is paid to the discussion of natural minerals: the patterns of the mineralogy of mantle titanium-bearing phases (rutile, FeTiO3 ilmenite, garnet, pyroxene, spinel and post-spinel phases, phases with ilmenite- and perovskite-type structures, armalcolite) are given, the likely mechanisms of titanium incorporation into mantle phases, as well as the limiting titanium concentrations in these phases are considered. The new experimental data on the composition and conditions of the formation of titanium-bearing minerals and their phase associations at different mantle depths is generalized: phase relations in Ti-bearing systems (MgO–SiO2–TiO2 ± Al2O3) and the influence of titanium on the parameters of the most important phase transformations under the conditions of the mantle are considered. Agreement of the experimental results with the natural data allows us to clarify the patterns of the interphase titanium partitioning and the minor-element composition of the Earth's deep geospheres. [ABSTRACT FROM AUTHOR]

Chemical and structural data of two Cu-rich coloradoite crystals from Kalgoorlie, Australia, are reported. Two grains with simple stoichiometries, i.e., Hg1 –xCuxTe with x ~0.30, and ~0.22, were characterized by single-crystal X-ray diffraction and electron-probe microanalysis. In the absence of single-crystal data it might be tempting to hypothesize that the presence of large amounts of other elements can induce some ordering leading to distinct mineral species. However, structural analyses show that all of the phases are cubic and crystallize in the space group . On the basis of information gained from the chemical and structural characterization it can be concluded that there is a complete solid solution between coloradoite and a possible, still unknown, Cu-coloradoite in nature. [ABSTRACT FROM AUTHOR]

An examination of a specimen of aguilarite from the type locality provides new data on the chemistry and structure of this mineral. The chemical formula of the crystal used for the structural study is (Ag3.98Cu0.02)(Se0.98S0.84Te0.18), on the basis of 6 atoms. The mineral was found to be monoclinic, crystallizing in space group P21/n, with a = 4.2478(2), b = 6.9432(3), c = 8.0042(5) Å , β = 100.103(2)º, V = 232.41(2) Å3 and Z = 4. The crystal structure [refined to R1 = 0.0139 for 958 reflections with I > 2σ(I)] is topologically identical to that of acanthite, Ag2S. It can be described as a body-centred array of tetrahedrally coordinated X atoms (X = S, Se and Te) with Ag2X3 triangles in planes nearly parallel to (010); the sheets are linked by the Ag1 silver site, which has twofold coordination. Aguilarite is definitively proved to be isostructural with acanthite; it does not have a naumannite-like structure, as previously supposed. Our data support the hypothesis that there are two solid solution series in the system: a monoclinic 'acanthite-like' series (from Ag2S-Ag2S0.4Se0.6), and an orthorhombic 'naumannite-like' series (from Ag2S0.3Se0.7-Ag2Se). This is supported by data gathered on synthetic counterparts. Aguilarite remains as a valid as a mineral species, but it should be described as the Se-analogue of acanthite. In this study we also (1) review the history of the aguilarite; (2) compare properties of synthetic and natural aguilarite; and (3) demonstrate how earlier researchers erred in describing aguilarite as orthorhombic. The Te-bearing composition of the studied aguilarite crystal suggests the possibility of a solid solution with cervelleite (Ag4TeS). [ABSTRACT FROM AUTHOR]

Schmitterite, UTeO5, was found in a sample of the mineralogical collection of the Natural History Museum of the University of Florence. The sample is from the Bambolla mine, Moctezuma, Sonora, Mexico and the mineral occurs as very rare crystals associated with emmonsite. Schmitterite is orthorhombic, space group Pca21, with the following unit-cell parameters: a = 10.163(1), b = 5.361(1), c = 7.865(1) Å, V = 428.5(1) Å3, and Z = 4. EDS chemical analyses showed only uranium and tellurium to be present. The crystal structure has been solved and refined to R = 2.28%. It consists of edge-sharing chains of UO7 pentagonal bipyramids parallel to [001] linked into a framework by TeO4 polyhedra. The crystal-chemical reasons for the choice of the non-centrosymmetric arrangement and the structural relationships with other natural tellurites are outlined. [ABSTRACT FROM AUTHOR]

Garavellite, FeSbBiS4, was found in a sample of the mineralogical collection of the Natural History Museum of the University of Florence. The sample is from the Cu–Fe deposit of Caspari, Saverland, North Rhine-Westphalia, Germany. Garavellite occurs as very rare, elongated prismatic crystals up to 100 µm in length, spatially associated with large berthierite crystals, bismuthinite, chalcopyrite, and siderite. It does not contain inclusions of or intergrowths with other minerals. Macroscopically garavellite is grey in colour and shows a grey-black streak. The Vickers hardness (VHN50) is 206 kg/mm2. In plane-polarized incident light garavellite is grey in colour, with distinct bireflectance. Reflectance percentages for R min and R max are 33.8, 41.8 (471.1 nm), 33.3, 40.9 (548.3 nm), 32.7, 39.5 (586.6 nm), and 32.4, 38.8 (652.3 nm), respectively. Garavellite is orthorhombic, space group Pnam, with the following unit-cell parameters: a = 11.413(1) Å, b = 14.164(1) Å, c = 3.759(1) Å, V = 607.7(2) Å3, and Z = 4. Electron microprobe analyses give the chemical formula Fe0.94Cu0.01As0.01Sb1.02Bi0.99S4.03. The crystal structure has been solved and refined to R = 2.38%. It consists of FeS6 octahedra forming edge-sharing chains parallel to [001] with the Sb3+ and Bi3+ cations inserted between the chains. The crystal-chemical relationships with berthierite as well as the different lone-pair stereochemical activities of antimony and bismuth in the two structures are discussed. [ABSTRACT FROM AUTHOR]

The pseudo-binary system CaMgSi2O6-KAlSi2O6, modeling the potassium-bearing clinopyroxene (KCpx) solid solution, has been studied at 7 GPa and 1,100–1,650 °C. The KCpx is a liquidus phase of the system up to 60 mol% of KAlSi2O6. At higher content of KAlSi2O6 in the system, grossular-rich garnet becomes a liquidus phase. Above 75 mol% of KAlSi2O6 in the system, KCpx is unstable at the solidus as well, and garnet coexists with kalsilite, Si-wadeite and kyanite. No coexistence of KCpx with kyanite was observed. Above the solidus, KAlSi2O6 content of the KCpx coexisting with melt increases with decreasing temperature. Near the solidus of the system (about 1,250 °C) KCpx contains up to 5.6 wt% of K2O, i.e. about 22–26 mol% of KAlSi2O6. Such high concentration of potassium in KCpx is presumably the maximal content of KAlSi2O6 in the Fe-free clinopyroxene at 7 GPa. In addition to the major substitution MgM1CаМ2⇔AlМ1KМ2, the KCpx solid solution contains Ca-Eskola and only minor Ca-Tschermack components. Our experimental results indicate that the natural assemblage KCpx+grossular-rich garnet might be a product of crystallization of the ultra-potassic SiO2-rich alumino-silicate mantle melts (>200 km). [ABSTRACT FROM AUTHOR]

Kudryavtsevaite, ideally Na3MgFe3+Ti4O12, is a new mineral from kimberlitic rocks of the Orapa area, Botswana. It occurs as rare prismatic crystals, up to 100 μm m across, associated with Mg-rich ilmenite, freudenbergite and ulvöspinel. Kudryavtsevaite is opaque with a vitreous lustre and shows a black streak. It is brittle; the Vickers hardness (VHN100) is 901 kg mm−2 (range: 876-925) (Mohs hardness ∼6). In reflected light, kudryavtsevaite is moderately bireflectant and very weakly pleochroic from dark grey to a slightly bluish grey. Under crossed polars, it is very weakly anisotropic with greyish-bluish rotation tints. Internal reflections are absent. Reflectance values (%),Rmin and Rmax, are: 21.3, 25.4 (471.1 nm), 20.6, 24.1 (548.3 nm), 20.0, 23.5 (586.6 nm) and 19.1, 22.4 (652.3 nm). Kudryavtsevaite is orthorhombic, space group Pnma, with a = 27.714(1), b = 2.9881(3), c = 11.3564(6) Å, V = 940.5(1) Å3, and Z = 4. The crystal structure [R1 = 0.0168 for 819 reflections with I > 2σ(I)] consists of edge-sharing and corner-sharing chains composed of Mg, Fe3+ and Ti atoms coordinated by six atoms of oxygen and running along the b axis, with Na filling the tunnels formed by the chains. The eight strongest powder-diffraction lines [d in Å (I/I0) (hkl)] are: 7.17 (100) (301), 4.84 (70) (302), 2.973 (35) (901), 2.841 (50) (004), 2.706 (50) (902), 2.541 (50) (312), 2.450 (70) (611), and 2.296 (45) (612). The average results of 12 electron microprobe analyses gave (wt.%): Na2O 16.46(15), CaO 1.01(3), MgO 5.31(5), Fe2O3 22.24(32), Cr2O3 1.05(6), Al2O3 0.03(2), TiO2 53.81(50), total 99.91, corresponding to the empirical formula (Na2.89Ca0.10)Σ2.99(Ti3.67Fe1.523+Mg0.72Cr0.08)Σ5.99O12, or ideally Na3MgFe3+Ti4O12. The new mineral has been approved by the IMA-CNMNC and named for Galina Kudryavtseva (1947-2006), a well known Russian mineralogist and founder of the Diamond Mineralogy Laboratory and scientific school for investigation of diamond mineralogy and geochemistry at the Lomonosov State University in Moscow, Russia. [ABSTRACT FROM AUTHOR]