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Cadoni M.,University of Turin | Ciriotti M.E.,Associazione Micromineralogica Italiana | Ferraris G.,University of Turin
Rendiconti Lincei | Year: 2011

Wakefieldite-(Y) with approximate composition (Y 0.40Nd 0.15Ce 0.15- Ca 0.15Th 0.15)(V 0.92As 0.08)O 4 is reported from an abandoned Fe- and Mn-ore mines located at Montaldo di Mondovì, Piedmont, Italy. The zircon-type crystal structure (space group I4 1/amd; a = 7.2591 Å , c = 6.4255 Å ) has been refined (R = 0.017 for 175 independent reflections) using X-ray diffraction data collected on a crystal from this locality. Our data confirm the validity of the species that previously had been only roughly defined using an impure pulverulent sample from Wakefield Lake (Quebec, Canada). The substantial (30%) joint replacement of Ca 2+ and Th 4+ for Y 3+ in the present wakefieldite-(Y) expands the cell volume of pure YVO 4 and could anticipate the existence of minerals with zircon-type structure and (A 0.5 2+A' 0.5 4+)T 5+O 4 composition. © Springer-Verlag 2011.

Oberti R.,CNR Institute of Geosciences and Earth Resources | Boiocchi M.,University of Pavia | Hawthorne F.C.,University of Manitoba | Camara F.,University of Turin | And 2 more authors.
Canadian Mineralogist | Year: 2015

The crystal-chemical characterization of an amphibole with an unusual composition, A(Na0.76K0.24)B(Ca1.42Na0.56Mn2+ 0.02) C(Mg2.64Fe2+ 1.95Mn2+ 0.07Mg2.64Zn0.01Fe3+ 0.01Ti4+ 0.32)T(Si7.18Al0.82)O22 W[(OH)0.58O0.27F1.15], found in pegmatitic veins at Kariasen, Larvik Plutonic Complex, Norway, provides an excellent example of the detection and estimation of the oxo component in amphibole. The use of Ti as a proxy for the oxo component is discussed and a procedure to derive accurate Ti partitioning from the results of structure refinement is described. Because the presence and amount of oxo component in amphiboles are important in order to determine values of fO2 and fH2O, especially in igneous and magmatic systems, this procedure should be applied any time the compositional data or the petrological context indicate the presence of significant Ti, or suggest that the oxo component may be a relevant issue.

Kampf A.R.,Natural History Museum of Los Angeles County | Mills S.J.,Khan Research Laboratories | Nestola F.,University of Padua | Ciriotti M.E.,Associazione Micromineralogica Italiana | Kasaasaasatkin A.V.,V O Almazjuvelirexport
American Mineralogist | Year: 2013

Saltonseaite, K3NaMn2+Cl6, is a new mineral from the Salton Sea, Imperial County, California, U.S.A., which formed as the result of the evaporation of geothermal (hydrothermal) brines enriched in K, Na, Mn, and Cl. It occurs as lozenge-shaped and bladed crystals to about 10 cm that are composites of parallel-grown {012} rhombohedra. It is associated with large, well-formed crystals of sylvite and halite. Crystals are transparent and colorless, but appear light orange due to inclusions of akaganéite. The streak is white and the luster is vitreous to oily, the latter being due to deliquescence. The Mohs hardness is about 21/2, the tenacity is brittle, the fracture is irregular, and crystals exhibit one very good cleavage on {110}. The mineral has an astringent taste and is markedly hygroscopic. The measured and calculated densities are 2.26(1) and 2.297 g/cm3, respectively. Saltonseaite is soluble in water at room temperature and crystallizes from solution above 52 °C. Optically, saltonseaite is uniaxial positive, with ω = 1.577(1) and ε = 1.578(1) (white light) and is non-pleochroic. Energy-dispersive spectroscopic analyses (average of 5) provided: K 28.79, Na 5.35, Mn 13.48, Fe 0.24, Cl 52.19, total 100.05 wt%. The empirical formula (based on 6 Cl atoms) is: K3.00Na0.95Mn 1.002+Fe0.022+Cl6. Saltonseaite is trigonal, R3̄c, with cell parameters a = 12.0966(5), c = 13.9555(10) Å, V = 1768.48(16) Å3, and Z = 6. The nine strongest lines in the X-ray powder diffraction pattern are [dobs in Å(I)(hkl)]: 5.83(61)(012); 3.498(25)(300); 2.851(68)(131); 2.689(32)(312); 2.625(62)(214); 2.542(100)(223); 1.983(32)(324); 1.749(20)(600), and 1.384(22)(multiple). The structure of saltonseaite (R1 = 1.08% for 558 Fo > 4σF) contains face-sharing chains of alternating Mn2+Cl6 octahedra and NaCl6 polyhedra along c. The chains are joined via bonds to eight-coordinated K atoms. Saltonseaite is isostructural with rinneite, K3NaFe2+Cl6, and very similar in structure with chlormanganokalite, K4Mn 2+Cl6. Existing chemical analyses for saltonseaite and rinneite fail to confirm a solid-solution series between them; experimental studies are needed.

Ciriotti M.E.,Associazione Micromineralogica Italiana
European Journal of Mineralogy | Year: 2015

Churchite-(Nd) and iodine, up to now recognized as valid minerals by IMA CNMNC, are discredited because, for different reasons, both are non-existent mineral species and were never actually characterized. Churchite-(Nd) is in fact neodymium-rich churchite-(Y) and iodine has never been found at its sole purported type locality of Vesuvius. Both discreditations have been approved by the IMA CNMNC (15-C and 15-D). © 2015 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart.

Bittarello E.,University of Turin | Camara F.,University of Turin | Ciriotti M.E.,Associazione Micromineralogica Italiana | Marengo A.,University of Turin
Mineralogy and Petrology | Year: 2015

Ottensite, Na3 (Sb2O3)(SbS3)·3H2O, brizziite, NaSbO3, and mopungite, NaSb(OH)6, have been found on several specimens from the antimony mine of Pereta (Grosseto, Tuscany, Italy). Ottensite from Pereta mine occurs as brilliant reddish-brown spheroidal aggregates, with a diameter up to 0.2 mm, formed by radially oriented individuals. These aggregates are associated with well-shaped tabular and pseudocubic colourless crystals of mopungite and platy aggregates of brizziite. This is the second world occurrence of ottensite and brizziite. The mineral species were characterized by electron microprobe analysis, X-ray diffraction study and microRaman spectroscopy. Single-crystal X-ray diffraction data were collected on a twinned crystal of mopungite and the structure was for the first time refined on a natural sample in space group P42/n [unit cell parameters a = 8.036(3) Å, c = 7.926(6) Å, V = 511.88(5) Å3, Z = 4] obtaining an R1-index of 5.17, wR2 of 13.52 and GooF of 1.247. © 2015, Springer-Verlag Wien.

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