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  • Author: A. Basso x
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Abstract

Crystal structure refinement was carried out on a defect spinel with composition Mg0.388Al2.408O4 synthesized at 2050°C Combining information from site occupancies and bond distances for tetrahedral and octahedral sites, the following cation and vacancy distribution were obtained: (Al0.653Mg0.347)(Al1.755Mg0.0410.204)O4. Structural analysis performed after heating the same crystal at 1150°C led to the same result, suggesting that the obtained distribution is stable over a wide range of temperatures.

Abstract

A crystallographic and crystal chemical study has been performed on a new mineral, an orthorhombic MnSO3 · 3H2O occurring in manganese ores at the Gambatesa Mine (Val Graveglia, Italy), associated with tephroite, bementite, braunite, hausmannite and hematite. Gravegliaite, appearing mainly as few radial aggregates of prismatic crystals, elongated parallel to [010] and up to 0.5 mm long, crystallizes in Pnma space group with a = 9.763(1) Å, b = 5.635(1) Å and c = 9.558(1) Å. It is colourless, transparent, optically biaxial and nonpleochroic with nα = 1.590, nβ = 1.596, nγ = 1.636 and 2 Vγ = 41° (Z = b). The strongest lines in the powder pattern are (d Å) 6.83, 4.33 and 3.43. Microprobe analyses reveal a good compositional homogeneity and a quasi-ideal chemical composition. The crystal structure refinement confirms this mineral to be the natural analogue of synthetic MnSO3 · 3H2O described by previous authors. The attempt to localize hydrogen atoms and to assign hydrogen bonds is discussed, since hydrogen bonds seem to play the major role in assuring cohesion to the structure.

Abstract

Reppiaite occurs in manganese ores at the Gambatesa Mine, near Reppia village (Val Graveglia, Italy), mainly associated with a Mn-sheet silicate and Mn – Ca-carbonates. It was found in small amounts of very minute tabular crystals, (100) flattened, grown in fracture. Reppiaite, with ideal formula Mn5(OH)4(VO4)2, crystallizes in C2/m space group with a = 9.604(2) Å, b = 9.558(2) Å, c = 5.393(1) Å and β = 98.45(1)°. The strongest lines in the X-ray powder pattern are d 13[unk] = 2.68 Å and d 200 = 4.76 Å. It is orange-red in colour, transparent, biaxial negative with 2 V large and slightly pleochroic. Microprobe analyses reveal a partial As substitution for V, leading to the empirical formula Mn5.01(OH)3.98[(V1.65-As0.35)O8.02]. The crystal structure of reppiaite is constructed of a quasi cubic close-packing of oxygens and hydroxyl groups, whose layers are stacked parallel to (100). The structure, refined to R = 0.038, consists of Mn octahedral layers bound together by isolated (V, As) tetrahedra and hydrogen bonds. Among the minerals, whose chemical formula has the same atomic proportions of reppiaite, only cornubite shows very similar structural features.

Environmental pollution by pesticide residues is a major environmental concern due to the extensive use of these substances in agriculture. The insecticide β-cyfluthrin is a synthetic pyrethroid widely used in agricultural and other domestic activities. The aim of the present study was to assess the genotoxic effects of a sublethal exposure of the fish Bryconamericus iheringii (Characidae) to a commercial formulation of β-cyfl uthrin using the comet assay. Fish were exposed to sublethal concentrations (4.2 and 5.6 μg/L) of β-cyfluthrin under static conditions during 24- and 48-h exposure periods. Fish in tap water were used as negative controls. Results obtained by the comet assay revealed genotoxic effects of the pyrethroid in the higher concentration and at the longer exposure period. The mean DNA damage index of fish exposed to 5.6 μg/L β-cyfluthrin for 48 h was significantly higher (145.9 ± 51.8) than in the control group (69.3 ± 39.5). These findings indicate that native fi sh species might be at risk for genotoxic damage in waters contaminated with β-cyfluthrin

Abstract

Specimens of Colominella (agglutinated Foraminifera) from a Pliocene Mediterranean succession were analysed through a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDX) to document their test microstructure. Colominella develops a complex large test with a mostly biserial chamber arrangement, but with the internal chamber lumens partitioned by vertical and horizontal plates that form a labyrinthine structure of alcoves. This internal partition occurs from the first chambers but is completely masked from the outside by the thick wall. The test-wall microstructure is characterized by canaliculi (parapores) that are externally covered by a pavement of agglutinated grains. The mineralogical characterization of the agglutinated grains and the secreted cement shows that the grains are strongly selected as regards to size, arrangement and composition, with the coarse grains placed close to the outer wall. Moreover, these coarse grains, forming a pavement, are made of monocrystalline quartz, whereas the inner part of the skeleton is mostly composed of dolomite. The carbonate cement is less abundant and appears as cloudy light grey areas among the detrital grains. These shell features can be interpreted as functional adaptations to perform kleptoplastidy and/or to house functional photosymbionts, probably induced by stable environmental conditions as in warm shallow waters characterized by low nutrient flux.