1,721,044 research outputs found
A contribution to the mineralogy of Sicily, Italy - Kintoreite from the Tripi mine, Peloritani Mountains: occurrence and crystal structure
No full textA new occurrence of kintoreite, ideally PbFe3(PO4)(PO3OH)(OH)(6), is described from the Tripi mine, Ali, Peloritani Mountains, northeastern Sicily, Italy. Kintoreite occurs as yellow equant crystals, up to 0.05 mm in size, on quartz, associated with another alunite-supergroup mineral currently under study. The studied grains of kintoreite are chemically zoned, showing the occurrence of two distinct domains. Electron microprobe analyses gave (in wt.%): SO3 5.47(27), P2O5 17.55(14), Al2O3 7.81(35), Fe2O3 23.81(44), PbO 35.11(41), H2Ocalc 9.93, total 99.68 (darker domains) and SO3 6.03(5), P2O5 16.66(23), Al2O3 4.22(2), Fe2O3 27.31(6), PbO 33.78(22), H2Ocalc 10.25, total 98.25 (brighter domains). On the basis of 14 O atoms per formula unit (apfu) and (P+S) = 2 apfu, the darker and brighter domains have chemical formula Pb-1.00(Fe1.893+Al0.97)(sigma 2.86)[P1.57S0.43O7.43(OH)(0.57)][(OH)(5.58)(H2O)(0.42)](sigma 6.00) and Pb-0.98(Fe2.213+Al0.53)(sigma 2.74)[P1.51S0.49O7.49(OH)(0.51)][(OH)(5.18)(H2O)(0.82)](sigma 6.00), respectively. Single-crystal X-ray diffraction was performed on a grain extracted from the same sample. Unit-cell parameters are a = 7.2191(10), c = 16.834(3) angstrom, V = 759.8(3) angstrom(3) and Z = 3; space group Rm. The crystal structure was refined on the basis of 226 unique reflections with F-o > 4 sigma(F-o) and 31 least-square parameters to R-1 = 0.0415. Kintoreite is isotypic with other alunite-supergroup minerals. Micro-Raman spectroscopy suggests the possible occurrence of H2O groups, supporting the possible protonation of (OH) groups as a charge-balance mechanism in this mineral. Kintoreite may play an environmental role in the Ali area, where previous authors detected high concentrations of potentially toxic elements in soils
Crystal chemistry and structural refinement of chromites from different chromitite layers and xenoliths of the Bushveld Complex.
No full textCrystal chemistry and structural refinement of 20 chromite crystals representative of different chromitites layers and xenoliths from the Critical Zone of the Bushveld Complex have been studied. Small differences in the structural parameters of chromites have been found along the Bushveld sequence and these allowed to discriminate two main subdivision between the Lower and Middle Group samples and the Upper Group and Merensky Reef samples. The small increase of chromite oxygen coordinates seems to be related with the decrease of cooling rates as estimated from the filling and cooling model for the Bushveld Complex proposed by Cawthorn & Walraven (1998). In fact, the cooling rates for Upper Group and Merensky Reef are smaller than that of Lower Group and Middle Group. Moreover, peculiar structural parameters have been found for chromites in the Tweefontein pipe suggesting different cooling rates.Peer reviewe
Crystal-chemistry of sulfates from the Apuan Alps, Tuscany, Italy. VIII. New data on khademite, Al(SO 4)F(H 2 O) 5
Full text linkKhademite, ideally Al(SO4)F(H2O)5, from the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy, has been characterised through quantitative electron microprobe analysis, micro-Raman spectroscopy and single-crystal X-ray diffraction. Khademite occurs as colourless to whitish tabular crystals, up to 5 mm. Electron microprobe analysis (in wt.%, average of 20 spot analyses) gave: SO3 35.43, Al2O3 21.27, F 6.92, H2Ocalc 39.73, sum 103.35, -O = F 2.92, total 100.43. On the basis of 10 anions per formula unit, assuming the occurrence of 5 H2O groups and 1 (F+OH) atom per formula unit, its chemical formula can be written as Al0.96S1.02O4[F0.84(OH)0.16]Σ1.00·5H2O. The Raman spectrum of khademite is characterised by the occurrence of vibrational modes of SO4 groups and by broad and strong bands due to the O-H stretching modes. Khademite is orthorhombic, space group Pcab, with unit-cell parameters a = 11.1713(2), b = 13.0432(3), c = 10.8815(2) Å, V = 1585.54(5) Å3 and Z = 8. The crystal structure refinement converged to R1 = 0.0293 on the basis of 2359 unique reflections with Fo > 4σ(Fo) and 152 refined parameters. The crystal structure of khademite is characterised by the alternation, along b, of two distinct kinds of {010} layers, one formed by [001] rows of isolated Al-centred octahedra, connected to each other through H bonds, and the other showing isolated SO4 groups. Along b, oxygen atoms belonging to SO4 groups act as acceptor of H bonds from H2O groups coordinating Al atoms. The new data improved the description of the H bonds in khademite and led us to discuss about the possible existence of its (OH)-analogue, rostite. In addition, Raman spectroscopic data were collected on the same crystal used for the crystal-chemical characterisation, allowing a comparison with previous results
Origin of ruthenium, osmium, iridium and iron oxides by progressive desolforation and oxidation of laurite in Nurali chromitites (Russia).
No full textPlatinum-group minerals from the zoned ultramafic intrusion of Uktus (Central Urals, Russia).
No full textRedefinition of coquimbite, AlFe3+3(SO4)6(H2O)126H2O
No full textCoquimbite, AlFe3+3(SO4)6(H2O)126H2O, was considered as a pure Fe3+ hydrated sulfate. However, previous mineralogical studies pointed out the occurrence of essential Al, occupying a distinct site in the crystal structure of this mineral. Through the critical re-examination of the available literature and new crystal-chemical data collected on a specimen from the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy, the chemical formula of coquimbite has been revised, taking into account the occurrence of Al. Coquimbite has a homeotypic relationship with paracoquimbite, Fe4(SO4)6(H2O)126H2O; both mineral species belong to the coquimbite group. On the contrary, aluminocoquimbite, Al2Fe2(SO4)6(H2O)126H2O, has a different topology and does not belong to that group
Progress in the knowledge of 'ruby silvers': New structural and chemical data of pyrostilpnite, Ag 3 SbS 3
No full textThe crystal structure of pyrostilpnite from the Plaka mine, Lavrion Mining District, Greece, was refined in the space group P21/c to a final R1 index of 0.0283 on the basis of 2047 reflections with Fo > 4σ(Fo) and 65 refined parameters. Unit-cell parameters of the crystal examined are a = 6.8629(6), b = 15.8800(14), c = 6.2711(5) Å, β = 117.087(2)°, V = 608.48(9) Å3 and Z = 4. Chemical data agree with the stoichiometric formula Ag3SbS3. The crystal structure reported previously was confirmed, although a higher precision of refinement was achieved. It can be described as formed by {010} slabs running along c and connected along a through relatively longer Ag-S bonds. The analysis of the atomic displacement parameters together with a refinement with higher order tensors in the expression of the structure factors revealed no hint for pyrostilpnite as an ionic conductor. A historical background of the 'ruby silvers' is also reported
Crystal-chemistry of micas belonging to the yangzhumingite-fluorophlogopite and phlogopite-fluorophlogopite series from the Apuan Alps (northern Tuscany, Italy)
No full textThe present work reports the crystal-chemical characterization of micas from the Monte Arsiccio and Buca della Vena mines (Apuan Alps, Italy) through electron microprobe analysis, single-crystal X-ray diffraction, and Raman spectroscopy. The sample from the Monte Arsiccio mine can be classifiedas an intermediate member of the yangzhumingite-fluorophlogopite series, with average crystal-chemical formula (K0.85Na0.01Ba0.09)Σ=0.95(Mg2.11Fe2+0.23Fe3+0.11Cr3+0.01Al0.20Ti0.04☐0.30)Σ=3.00(Si3.20Al0.80)Σ=4.00O10.00F1.90Cl0.02(OH)0.08. Unit-cell parameters are a ~ 5.30, b ~ 9.18, c ~ 10.14 Å, β ~ 100.12°, V ~ 486.22 Å3, corresponding to the 1M polytype. Structure refinements, performed in C2/m space group, converged to R1 = 3.54 and 4.46% and provided Mg plus Fe occupancy in the range 86–94% for the octahedral M1 and M2 sites. Raman spectroscopy shows very weak bands in the OH stretching region at ~ 3690 and 3580 cm−1. The sample from the Buca della Vena mine has been identified as an (OH)-rich fluorophlogopite, with average crystal-chemical formula (K0.84Na0.02Ca0.01)Σ=0.87(Mg2.12Fe2+0.55Fe3+0.10Al0.18☐0.05)Σ=3.00(Si2.99Al1.01)Σ=4.00O10.00F1.02Cl0.09(OH)0.89. Its unit-cell parameters are a ~ 5.33, b ~ 9.22, c ~ 10.23 Å, β ~ 100.09°, V ~ 494.39 Å3. Structure refinements gave good R1 values (3.27 and 4.37%) and revealed octahedral occupancy of 82–84% Mg and 16–18% Fe. Strong Raman signals at ~ 3702 cm−1 and 3595 cm−1 were observed in the OH stretching region. The findings allow to better understand not only the mineralogy of the Apuan Alps but, more generally, the crystal chemical details of intermediate dioctahedral-trioctahedral mica belonging to the yanzhumingite-fluorophlogopite series
New data on melanostibite, Mn2Fe3+Sb5+O6
No full textFollowing the identification of a new occurrence of melanostibite from the Apuan Alps, the crystal chemistry of this mineral has been re-examined using specimens from its type locality, Sjogruvan, orebro County, Sweden, and from the new occurrence, the Scortico-Ravazzone Mn ore deposit, Apuan Alps, Tuscany, Italy. Both specimens were examined through electron microprobe analysis, micro-Raman spectroscopy and single-crystal X-ray diffraction data; Mossbauer spectroscopy was used for the Swedish specimen. Electron microprobe data indicate a close to ideal composition Mn2Fe3+Sb5+O6 for both samples, whereas Mossbauer spectroscopy confirmed the trivalent oxidation state of Fe. Single-crystal X-ray diffraction for the Swedish and Italian specimens points to the acentric nature of melanostibite, space group R3. Refined unit-cell parameters of melanostibite from Scortico-Ravazzone and Sjogruvan are a = 5.2351(3), c = 14.3645(8) angstrom, V = 340.93(4) angstrom(3), and a = 5.2314(2), c = 14.3518(8) angstrom, V = 340.15(3) angstrom(3), respectively. Melanostibite is an homeotypic derivative of pyrophanite
- …
