1,720,990 research outputs found
Crystal-chemistry of tetrahedrite group minerals from the Apuan Alps hydrothermal ores (Tuscany, Italy)
No full textMonte Amiata: the mineralogical collection of the Natural History Museum of the Pisa University
No full textThe development and preservation of mineral collections from Tuscan occurrences for research,
education, and public exhibitions is one of the missions of the Natural History Museum of the Pisa University.
The regional collections are composed by a total of 8238 specimens, representing about 42% of the total
mineralogical collections.
The Monte Amiata collection, formed by 171 specimens, is one of the smallest among the regional
collections. Several specimens are accompanied by old hand-written labels dating back to the period of
activity of Prof. Antonio D’Achiardi (1839-1902) and were described by this author in his Mineralogia della
Toscana (D’Achiardi, 1872/73).
The specimens belong to three different groups: i) minerals from the Plio-quaternary hydrothermal ore
deposits, ii) minerals related to the volcanic rocks of the Monte Amiata, and iii) specimens formed through
the action of silica-rich waters.
The first group is representative of one of world-class Hg ore deposits of Monte Amiata (e.g., Rimondi et
al., 2015). The mining activity definitively ceased at the end of 1970s and since then the opportunity to
collect new specimens has progressively decreased. Consequently, old specimens kept in public or private
mineralogical collections are useful for the study of the mineralogy as well as the ore geology of the Monte
Amiata. The collection preserves several specimens of cinnabar representive of its different kinds of
occurrence in the mining district. Moreover, accessory minerals are present, such as metacinnabar, realgar,
orpiment, and stibnite. The occurrence of the high T cubic polymorph of HgS is particularly interesting
because its presence was not reported so far in literature. The recent study of some specimens kept in the
collection of the Natural History Museum led to the full characterization of metacinnabar from the
hydrothermal Hg ores from Monte Amiata.
Minerals related to the volcanic rocks have a particular historical importance, having been collected in the
first half of the XIX Century. For example, several loose crystals of sanidine were collected by the naturalist
Giorgio Santi (1746-1822). Santi (1795) described (and probably collected) also specimens of “fiorite”, a
variety of opal from Santa Fiora. These specimens, together with samples of diatomaceous earths, form the
third group of specimens constituting the Monte Amiata collection.
In conclusion, the collection is the proof of the mining exploitation carried out in the Monte Amiata area
and it has a great historical importance in housing several specimens collected between the end of the XVIII
and the beginning of the XIX Century. In this way, the collection is important not only from the scientific point
of view but also from an educational perspective, illustrating the evolution of the scientific knowledge and the
birth of the mineralogical school at the Pisa University
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
Tetrahedrite-(Hg), a new 'old' member of the tetrahedrite group
Full text linkTetrahedrite-(Hg), Cu6(Cu4Hg2)Sb4S13, has been approved as a new mineral species using samples from Buca della Vena mine (hereafter BdV), Italy, Jedová hora (Jh), Czech Republic and RoŽÅ 1/2ava (R), Slovakia. It occurs as anhedral grains or as tetrahedral crystals, black in colour, with metallic lustre. At BdV it is associated with cinnabar and chalcostibite in dolomite veins. At Jh, tetrahedrite-(Hg) is associated with baryte and chalcopyrite in quartz-siderite-dolomite veins; at R it is associated with quartz in siderite-quartz veins. Tetrahedrite-(Hg) is isotropic, greyish-white in colour, with creamy tints. Minimum and maximum reflectance data for Commission on Ore Mineralogy wavelengths in air (BdV sample), R in %) are 32.5 at 420 nm; 32.9 at 546 nm; 33.2 at 589 nm; and 30.9 at 650 nm. Chemical formulae of the samples studied, recalculated on the basis of 4 (As + Sb + Bi) atoms per formula unit, are: (Cu9.44Ag0.07)Σ9.51(Hg1.64Zn0.36Fe0.06)Σ2.06Sb4(S12.69Se0.01)Σ12.70 (BdV), Cu9.69(Hg1.75Fe0.25Zn0.06)Σ2.06(Sb3.94As0.06)S12.87 (Jh) and (Cu9.76Ag0.04) Σ9.80(Hg1.83Fe0.15Zn0.10)Σ2.08(Sb3.17As0.58Bi0.25)S13.01 (R). Tetrahedrite-(Hg) is cubic, I3m, with a = 10.5057(8) Å, V = 1159.5(3) Å3 and Z = 2 (BdV). Unit-cell parameters for the other two samples are a = 10.4939(1) Å and V = 1155.61(5) Å3 (Jh) and a = 10.4725(1) Å and V = 1148.55(6) Å3 (R). The crystal structure of tetrahedrite-(Hg) has been refined by single-crystal X-ray diffraction data to a final R1 = 0.019 on the basis of 335 reflections with Fo > 4σ(Fo) and 20 refined parameters. Tetrahedrite-(Hg) is isotypic with other members of the tetrahedrite group. Mercury is hosted at the tetrahedrally coordinated M(1) site, along with minor Zn and Fe. The occurrence of Hg at this position agrees both with the relatively large M(1)-S(1) bond distance (2.393 Å) and the refined site scattering. Previous occurrences of Hg-rich tetrahedrite and tetrahedrite-(Hg) are reviewed, and its relations with other Hg sulfosalts are discussed
Kerr Nonlinearity Dominance Diagnostic for Polarization-Dependent Loss Impaired Optical Transmissions
No full textWe present a method to classify optical transmission systems as linear or nonlinear based solely on signal-to-noise ratio statistics in presence of PDL-induced time-varying-performance. It obtains excellent accuracy (>95%), and it is proven accurate and robust under all the investigated conditions
Tellurium-rich stibiogoldfieldite and Se-bearing dantopaite from Goldfield, Nevada, U.S.A.: new crystal chemical data
No full textCotype material of stibiogoldfieldite from the Mohawk mine, Goldfield, Nevada, U.S.A., has been examined in order to collect single-crystal X-ray diffraction data of Te-rich stibiogoldfieldite and to characterize the associated Ag–Bi–(S,Se) phase. Tellurium-rich stibiogoldfieldite, with empirical formula (Cu11.30Ag0.03)Σ11.33(Sb0.80As0.57Bi0.06Te2.57)Σ4.00(S12.83Se0.20)Σ13.03, is cubic, space group I-43m, with unit-cell parameters a = 10.2947(3) Å, V = 1091.04(10) Å3. Its crystal structure has been refined to R1 = 0.0161 for 397 unique reflections with Fo > 4σ(Fo) and 25 refined parameters. The structure refinement confirmed the occurrence of vacancy at the M(2) site, in agreement with the substitution M(2)Cu+ + X(3)(Sb/As)3+ = M(2)□ + X(3)Te4+. The Ag–Bi–(S,Se) phase was identified as the 6P homologue of the pavonite series, namely dantopaite. Its empirical formula is Cu1.36Ag4.39Pb0.12Bi12.62Sb0.06(S14.01Se7.91Te0.08), showing an exceptionally high Se content.
Unit-cell parameters of Se-bearing dantopaite are a = 13.518(2), b = 4.0898(6), c = 18.984(3) Å, β = 106.816(6)°, V = 1004.7(3) Å3, space group C2/m. The crystal structure was refined to R1 = 0.0504 for 1230 unique reflections with Fo > 4σ(Fo) and 82 refined parameters. The metal excess (~ 0.55 atoms per formula unit) of this pavonite homologue is mainly due to the accumulation of Ag and Cu in the thin slab of the crystal structure, whereas the high Se content is related to the partial replacement of S preferentially occurring in the thick PbS-like slab. Selenium- and Pb-richer domains of dantopaite, with empirical formula Cu0.89Ag4.50Pb0.49Bi12.53Sb0.07(S11.26Se10.74), were also identified, as grains up to 30 μm in size intimately intergrown with bohdanowiczite, indicating the possibility of a wide Se-to-S substitution in dantopaite
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Tetrahedrite-(Cu), Cu12Sb4S13, from Bankov near Košice, Slovak Republic: A new member of the tetrahedrite group minerals
Full text linkTetrahedrite-(Cu), Cu12Sb4S13, was approved as a new mineral species from the Bankov magnesite deposit near Koxˇice, Slovak Republic where it occurs as anhedral grains, up to 0.4 mm across, associated with skinnerite, chalcostibite, famatinite, tetrahedrite-(Fe) and zoned aggregates of tennantite-(Cu) to tennantite-(Fe). Tetrahedrite-(Cu) is steel-grey, with metallic luster. Mohs hardness is ca. 31/2 - 4, calculated density is 5.029 g.cm-3. In reflected light, tetrahedrite-(Cu) is isotropic, grey with bluish shade. Reflectance data for the four COM wavelengths in air are [λ (nm): R (%)]: 470: 31.1; 546: 30.1; 589: 29.9; 650: 28.1. The empirical formula, based on electron-microprobe data (mean of 17 spot analyses), is Cu11.42Zn0.26Fe0.19(Sb4.06As0.08)Σ4.14S12.99. The ideal formula is Cu6(Cu4Cu2)Sb4S13, which requires (in wt.%) Cu 45.76, Sb 29.23 and S 25.01, total 100.00. Tetrahedrite-(Cu) is cubic, I 3m, with unit-cell parameters a = 10.3296(15) Å, V = 1102.2(5) å3, Z = 2. Its crystal structure was refined by single-crystal X-ray diffraction data to a final R1= 0.0347 on the basis of 261 unique reflections with Fo> 4σ(Fo) and 22 refined parameters. Tetrahedrite-(Cu) is isotypic with other tetrahedrite-group minerals. Previous findings of tetrahedrite-(Cu) are reported and some nomenclature issues, related to the Fe and Cu oxidation states, are 4 discussed. At the Bankov deposit, tetrahedrite-(Cu) is related to hydrothermal, most probably Alpine, solutions strongly enriched in Cu, Sb and S
- …
