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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
Granato di Campo ai Peri. Un nuovo ritrovamento nelle metabasiti dell'Elba Centrale
No full textL’Isola d’Elba è nota per la presenza di diverse località che hanno fornito campioni di granato, talvolta di buon livello
estetico. Oltre alla spessartina dei filoni pegmatitici e all’andradite delle mineralizzazioni ferrifere di Capo Calamita,
ritrovamenti più modesti sono legati alle rocce dei complessi ofiolitici. Da questo tipo di giacitura provengono anche gli esemplari descritti in questo articolo
Late Cretaceous black shales from the tuscan sedimentary succession (northern Tuscany, Italy): Geochemistry and ore mineralogy
No full textWe report on the first geochemical and mineralogical study of the Late Cretaceous black shales and black phyllites occurring within the basal portion of the “Scaglia toscana” and “Scisti sericitici” formations, respectively (Northern Apennines, northern Tuscany, Italy). The black shales occurring within the “Scaglia toscana” Formation are interbedded with red and greenish shales and form cm-thick layers; in some localities they are characterized by the occurrence of cm-sized pyrite nodules. Black phyllites and meta-cherts in the “Scisti sericitici” Formation are associated with Cu ores and with a small pyrite-molybdenite mineralization. These rocks are made of variable amounts of quartz, “chlorite”, illite/muscovite, pyrite ± calcite ± albite plus accessory amounts of baryte, apatite, sulfides and sulfosalts. In addition, they contain abundant carbonaceous matter (2-12 wt% total organic carbon). Whole-rock analyses by ICP-MS reveal a marked enrichment of Cd, Ag, Zn, Sb, Cu, Mo, V, Pb, and Tl with respect to the average marine shale and to the more typical shales of the “Scaglia toscana” Fm. The distribution of these elements in the studied samples is compatible with a strongly anoxic and euxinic depositional environment. The hyper-enrichment of Cd, Ag, Zn, Sb and Cu strongly suggests that besides from seawater these elements were extracted from additional sources, most likely hydrothermal vents
Nuovi minerali italiani. Le approvazioni 2017
No full textLa grande complessità geologica della nostra penisola è all'rogine del grande numero di specie mineralogiche nuove descritte per la prima volta al mondo in Italia. Nel corso del 2017, altre nuove specie con località tipo italian, descritte brevemente in questo articolo, sono state approvate dalla Commission on New Minerals, Nomenclature and Classification dell'International Mineralogical Association
Tourmalines from San Piero in Campo and other minor occurrences from the Elba Island - Le tormaline di San Piero in Campo e le altre giaciture minori dell'Isola d'Elba
No full textField trip to a well exposed LCT gem-pegmatite dyke swarm that developed at the contact between the slightly peraluminous Monte Capanne monzogranite pluton and its contact aureole. It is one of the youngest LCT gem-pegmatite complexes in the planet (6.9 Ma). Thanks to the very young age, the petrologic study of these rocks avoided the usual problems encountered in old systems (difficulties in the application of radiogenic isotope systematics to to error propagation with age; tectonic-metamorphic-hydrothermal reworking, etc.). For these reasons, the petrologic comparison of pegmatites with the potential monzogrante and leucogranite parets was possible, providing us with important insights on the behavior of these systems. Additionally, the overall small size of these pegmatite dikes allows for the study of structure, texture, mineralogy and geochemistry at a more manageable scale than in most large LGT pegmatites. The large number of pegmatitic dykes showing different degrees of geochemical evolution and the various types of host rocks allowed the development of variable compositions in tourmaline crystals, resulting in the occurrence of a quite large number of species
Nomenclature and classification of the spinel supergroup
Full text linkA new, IMA-approved classification scheme for the spinel-supergroup minerals is here reported. To belong to the spinel supergroup, a mineral must meet two criteria: (i) the ratio of cation to anion sites must be equal to 3:4, typically represented by the general formula AB2X4 where A and B represent cations (including vacancy) and X represents anions; (ii) its structure must comprise a heteropolyhedral framework of four-fold coordination polyhedra (TX4) isolated from each other and sharing corners with the neighboring six-fold coordination polyhedra (MX6), which, in turn, share six of their twelve X-X edges with nearest-neighbor MX6. Regardless of space group, the X anions form a cubic close-packing and each X anion is bonded to three M-cations and one T-cation. The fifty-six minerals of the spinel supergroup are divided into three groups on the basis of dominant X anion: O2– (oxyspinel), S2– (thiospinel), and Se2– (selenospinel). Each group is composed of subgroups identified according to the dominant valence and then the dominant constituent (or heterovalent pair of constituents) represented by the letter B in the formula AB2X4. The oxyspinel group (33 species) can be divided into the spinel subgroup 2-3 (A2+B3+2O4) and the ulvöspinel subgroup 4-2 (A4+B2+2O4) , the thiospinel group (20 species) into the carrollite subgroup 1-3.5 (A1+B3.5+2S4) and the linnaeite subgroup 2-3 (A2+B3+2S4) , finally, the selenospinel group (3 species) into the bornhardtite subgroup 2-3 (A2+B3+2Se4) and the potential “tyrrellite subgroup” ( A1+B3.5+2S4 , currently composed by only one species). Once the subgroup is established based on the valence of B, then the mineral species is identified by the combination of the dominant A- and B-cations. Moreover, the present nomenclature redefines the ideal formulae of titanomaghemite, cuprorhodsite, malanite, maghemite, filipstadite, tegengrenite, rhodostannite, toyohaite and xingzhongite as well as discredits “iwakiite”, “hydrohetaerolite” and “ferrorhodsite”
Micro-Raman spectroscopy of selected Mo minerals from Su Seinargiu (Sardinia, Italy)
No full textRaman spectra of selected molybdenum minerals, represented both by bismuth-molybdenum oxides (sardignaite, gelosaite, and mambertiite) and by molybdates [tancaite-(Ce), ichnusaite, nuragheite, and suseinargiuite] from the Su Seinargiu Mo-Bi prospect (Sardinia, Italy) are reported. Raman spectra were collected using samples previously characterized through X-ray diffraction and electron-microprobe analyses. Bismuth-molybdenum oxides are mainly characterized by bands in the range between 300 and 1000 cm-1, related to stretching modes of Mo-O and to Bi-O bonds. Bands related to O-H stretching modes were observed in the range between 3000 and 4000 cm-1. Raman spectra of molybdates are characterized by the four fundamental modes of MoO4 groups occurring between 250 and 1000 cm-1. Additionally, stretching bands related to O-H bonds were observed in tancaite-(Ce). Micro-Raman spectroscopy is an efficient tool for the discrimination of these rare phases, with some exceptions discussed in the text
Brattforsite, Mn19(AsO3)12Cl2, a new arsenite mineral related to magnussonite, from Brattforsgruvan, Nordmark, Värmland, Sweden
No full textBrattforsite is an approved mineral (IMA2019-127), with ideal formula Mn19(AsO3)12Cl2. Associated minerals in the type specimen from the Brattfors mine, Nordmark (Värmland, Sweden) include jacobsite, alleghanyite, phlogopite, calcite and dolomite. Brattforsite, forming subhedral, mostly equant crystals up to 0.5 mm across, is orange to reddish-brown with a white streak, and translucent with a resinous to vitreous lustre. The fracture is uneven to subconchoidal, and no cleavage is observed. It is very weakly pleochroic in yellow, optically biaxial (–) with 2V = 44(5)° and has calculated mean refractive index of 1.981. Measured and calculated density values are 4.49(1) and 4.54(1) g·cm− 3, respectively. Chemical analyses yields (in wt%): MgO 0.62, CaO 1.26, MnO 48.66, FeO 0.13, As2O3 46.72, Cl 2.61, H2Ocalc 0.07, O ≡ Cl –0.59, sum 99.49, corresponding to the empirical formula (Mn17.67Ca0.58Mg0.40Fe0.05)∑18.70As12.17O35.90Cl1.90(OH)0.20, based on 38 (O + Cl + OH) atoms per formula unit. The five strongest Bragg peaks in the powder X-ray diffraction pattern are [d (Å), I (%), (hkl)]: 2.843,100, (4 - 44); 2.828, 99, (444); 1.731, 32, (880); 2.448, 28, (800); 1.739, 25, (088). Brattforsite is monoclinic and pseudotetragonal, space group I2/a, with unit-cell parameters a = 19.5806(7), b = 19.5763(7), c = 19.7595(7) Å, β = 90.393(3)°, V = 7573.9(5) Å3 and Z = 8. The crystal structure was solved and refined to an R1 index of 3.4 % for 7445 reflections [Fo > 4σ(Fo)]. Brattforsite has the same overall structural topology as magnussonite (i.e., the species can be considered as homeotypic), but with 12 independent tetrahedrally coordinated As sites and 21 Mn sites with varying (4–8) coordination. The Mn-centered polyhedra, bonded through edge- and face-sharing, give rise to a three-dimensional framework. The (AsO3)3− groups are bonded to this framework through corner- and edge-sharing. Spectroscopic measurements (optical absorption, Raman, FTIR) carried out support the interpretation of the compositional and structural data
The crystal structure of alstonite, BaCa(CO3)2: An extraordinary example of 'hidden' complex twinning in large single crystals
Full text linkAlstonite, BaCa(CO3)2, is a mineral described almost two centuries ago. It is widespread in Nature and forms magnificent cm-sized crystals. Notwithstanding, its crystal structure was still unknown. Here, we report the crystal-structure determination of the mineral and discuss it in relationship to other polymorphs of BaCa(CO3)2. Alstonite is trigonal, space group P31m, with unit-cell parameters a = 17.4360(6), c = 6.1295(2) Å, V = 1613.80(9) Å3 and Z = 12. The crystal structure was solved and refined to R1 = 0.0727 on the basis of 4515 reflections with Fo > 4σ(Fo) and 195 refined parameters. Alstonite is formed by the alternation, along c, of Ba-dominant and Ca-dominant layers, separated by CO3 groups parallel to {0001}. The main take-home message is to show that not all structure determinations of minerals/compounds can be solved routinely. Some crystals, even large ones displaying excellent diffraction quality, can be twinned in complex ways, thus making their study a crystallographic challenge
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