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Ordered distribution of Cu and Ag in the crystal structure of balkanite, Cu9Ag5HgS8
Full text linkThe crystal structure of balkanite from the San Giovanni mine, Sardinia, Italy, has been solved by X-ray single-crystal diffraction on the basis of 883 reflections with Fogt;4σFo, with a final R1 = 0.055. Balkanite is monoclinic, space group P2/m, with unit-cell parameters a = 9.5539(11), b = 3.9150(4), c = 10.6424(12) Å, β = 90.047(9)°, V = 398.06(8)Å3. Its formula derived through the single-crystal structure refinement is Cu9.00Ag4.73Hg1.00S8, with Z = 1. Electron-microprobe analysis gave the formula (Cu8.69Fe0.12Zn0.08Ni0.07)σ8.96Ag4.63Hg0.93S8, close to the ideal formula (Cu8.70Me2+0.30)Ag4.70HgS8, or (Cu9-xMe2+x)Ag5-xHgS8, with x = 0.3. Although balkanite is not a layered compound, its crystal structure can be described as formed by the alternation, along a, of Cu-pure and Ag-rich layers. Additionally, it can also be described as based on two different alternating (010) atomic layers with all atoms on special positions (at y = 0 and), having chemical composition [Cu4Ag3HgS4]+ and [Cu5Ag2S4]-, or as formed by the alternation of two (10-1) polyhedral layers, having composition [Cu7Ag3S4]2+ and [Cu2Ag2HgS4]2-. Hg is linearly coordinated, Ag assumes a tetrahedral or a distorted octahedral coordination, whereas Cu displays a linear or planar triangular coordination. A critical comparison with the related mineral danielsite, ideally (Cu,Ag)14HgS8, is also presented
A crystallographic excursion in the extraordinary world of minerals: the case of Cu- and Ag-rich sulfosalts
Full text linkCopper and silver are common constituents in natural sulfosalts and can be present as minor or major components. Owing to the different kinds of coordination they can assume, these elements give rise to a number of sulfosalts that are usually quite complex to describe from a structural point of view because of the presence of twinning, disorder, polytypism and sometimes incommensurate modulation. Moreover, it is common to find them in different, partially occupied split sites, favoring the presence of strong ionic conductivity that can be related to a number of interesting technological properties. In this regard, a series of Cu- and Ag-rich sulfosalts showing an excess of these cations with respect to As, Sb and Bi is particularly interesting. Their crystal structures as well as their potential interest for materials science and solid-state physics are outlined. Copper- and mixed (Cu, Ag)-sulfosalts belonging to the wittichenite, tetrahedrite, galkhaite, routhierite and nowackiite series are discussed, together with some related compounds. Whereas in the wittichenite series Cu has either a trigonal planar or tetrahedral coordination, in members of the other series this element forms three-dimensional tetrahedral frameworks giving rise to cavities hosting other cations and anions. More difficult is the description of Ag-rich sulfosalts owing to the highly variable coordination environments shown by this element. Structural features of selected Ag sulfosalts together with members of the argyrodite series are discussed, highlighting the particular properties derived from the behavior of Ag
Fluorite-related one-dimensional units in natural bismuth oxysulfates: The crystal structures of Bi14O16(SO4)5 and Bi30O33(SO4)9(AsO4)2
No full textThe crystal structures of two new natural Bi oxysulfates with the formula Bi14O16(SO4)5 [labelled new phase I; monoclinic, space group C2, a = 21.658 (4), b = 5.6648 (9), c = 15.092 (3) A ̊ , = 119.433 (11) and Z = 2] and Bi30O33(SO4)9(AsO4)2 [labelled new phase II; triclinic, space group P1, a = 5.670 (3), b = 13.9408 (9), c = 22.7908 (18) A ̊ , = 80.903 (5), = 82.854 (14), = 78.27 (2) and Z = 1] from the high-temperature fumarole deposit of the La Fossa crater at Vulcano (Aeolian Islands, Italy) are reported. The structures are built up by a combination of fluorite-related Bi—O units and isolated (SO4)2
tetrahedra (new phase I) or both (SO4)2and (AsO4)3tetrahedra (new phase II). Owing to the effect of stereoactive lone pairs of Bi3+, Bi—O units in both thestructures can be suitably described in terms of oxo-centered OBi4 tetrahedra. The structure of Bi14O16(SO4)5 is based upon one-dimensional [O16Bi14]10+ribbons formed by six chains of edge-sharing OBi4 tetrahedra extending along [010]. In the structure of Bi30O33(SO4)9(AsO4)2 the same ribbon type coexists with another one-dimensional ribbon formed by seven chains of edge-sharing OBi4 tetrahedra and with the composition [O17Bi16]14+. Ribbons of the same type are joined by (SO4)2and (AsO4)3tetrahedra along [010] – if a reduced triclinic unit-cell setting is considered – so forming two different (001) slabs which alternate to each other along [001] and are joined by additional (SO4)2 tetrahedra. New phase I represents the natural analogues of synthetic Bi14O16(SO4)5, but with an ordered structure model
Crystal chemistry of mercury sulfosalts - Galkhaite, (Hg<inf>5+x</inf>Cu<inf>1-x</inf>)Cs<inf>1-x</inf>As<inf>4</inf>S<inf>12</inf> (x ≈ 0): Crystal structure and revision of the chemical formula
No full textThree specimens of galkhaite from the Getchell mine (G), Nevada, USA; the Gal-Khaya As-Hg-Sb deposit (Gk), Yakutia, Russia; and Signols (S), Piedmont, Italy, have been fully characterized through single-crystal X-ray diffraction and electronmicroprobe analyses. Chemical data indicate the formulae [(Hg4.61Zn0.38Fe0.04)Σ5.03(Cu1.03Ag0.04)Σ1.07]Σ6.10(Cs0.76Tl0.20)Σ0.96(AS3.81Sb0.04)Σ3.85S12.06 (G), [(Hg4.66Zn0.32)Σ4.98(Cu0.55Ag0.45)Σ1.00]Σ5.98(Cs0.74Tl0.06(As3.42Sb0.56)Σ3.98S12.05 (Gk), and [(Hg4.10Zn0.85)Σ4.95(Cu0.89Ag0.16)Σ1.05]Σ6.00Cs0.95As3.64Sb0.16)Σ3.80 S12.19 (S). Unit-cell parameters are a 10.405(3) Å (G), 10.443(1) Å (Gk), and 10.332(2) Å (S), space group I4 ̄3m. The crystal structure of the three specimens has been solved to R1 = 0.029 (G), 0.028 (Gk), and 0.031 (S). It is a three-dimensional framework of HgS4 and AsS3 polyhedra, with Cs hosted in large 12-fold coordinated cavities. The introduction of Cs+, as well as minor Tl+ , at these structural positions requires the replacement of Hg2+ by Cu+ . The mixed site occupancy at the Hg site of galkhaite is a case of valency-imposed double site-occupancy. Consequently, the idealized chemical formula of galkhaite can be written as (Hg5Cu)CsAs4S12. Taking into account the possible existence of vacancy in the structural cavities, the formula can be generalized as (Hg5+xCu1-x)Σ6Cs1-xAs4S12 (x ≈ 0)
Ralphcannonite, AgZn2TlAs2S6, a new mineral of the routhierite isotypic series from Lengenbach, Binn Valley, Switzerland
Full text linkThe new mineral species ralphcannonite, AgZn2TlAs2S6, was discovered in the Lengenbach quarry, Binn Valley, Wallis, Switzerland. It occurs as metallic black equant, isometric to prismatic crystals, up to 50 μm, associated with dufrenoysite, hatchite, realgar and baryte. Minimum and maximum reflectance data for COM wavelengths in air are [λ (nm): R (%)]: 471.1: 25.8/27.1; 548.3: 25.2/26.6; 586.6: 24.6/25.8; 652.3: 23.9/24.8. Electron microprobe analyses give (wt.%): Cu 2.01(6), Ag 8.50( 16), Zn 10.94(20), Fe 3.25(8), Hg 7.92(12), Tl 24.58(26), As 18.36(19), Sb 0.17(4), S 24.03(21), total 99.76(71). On the basis of 12 atoms per formula unit, the chemical formula of ralphcannonite is Ag0.63(2)Cu0.25(2)Zn1.35(5)Fe0.47(1)Hg0.32(2)Tl0.97(3)[As1.97(6)Sb0.01(1)]Σ1.9(8)S6.03(8). The new mineral is tetragonal, space group I4 2m, with a =9.861 (2), c= 11.125(3) Å, V= 1081.8(4) Å3, Z= 4. The main diffraction lines of the calculated powder diagram are [d(in Å), intensity, hkl]: 4.100, 85, 211; 3.471,40, 103; 2.954, 100, 222; 2.465, 24, 400; 2.460,39, 303. The crystal structure of ralphcannonite has been refined by X-ray single-crystal data to a final Ri =0.030, on the basis of 140 observed reflections [F0> 4σ(F0)]. It shows a three dimensional framework of (Ag,Zn)- centred tetrahedra (1 M1 + 2 M2), with channels parallel to [001] hosting TlS6 and (As5Sb)S3 disymmetric polyhedra. Ralphcannonite is derived from its isotype routhierite M1iCuM2Hg2TlAs2S6 through the double heterovalent substitution M1Cu+ + M2Hg2+→ M1Zn2+ + M2Ag+. This substitution obeys a steric constraint, with Ag+, the largest cation relative to Zn2+ and Cu+, entering the largest Ml site, as observed in arsiccioite. The ideal crystal-chemical formula of ralphcannonite is M1ZmM2(Zn0.5Ag0.5)2TlAs2S6
Lead-antimony sulfosalts from Tuscany (Italy). XVI. Carducciite, (AgSb)Pb6(As,Sb)8S20, a new Sb-rich derivative of rathite from the Pollone mine, Valdicastello Carducci: Occurrence and crystal structure
Full text linkThe new mineral species carducciite, (AgSb)Pb6(As,Sb)8S20, has been discovered in the baryte-pyrite-(Pb-Ag-Zn) deposit of the Pollone mine, near Valdicastello Carducci, Apuan Alps, Tuscany, Italy. It occurs as black metallic prismatic crystals, up to 0.5 mm long, associated with pyrite and sterryite. Its Vickers hardness (VHN10) is 61 kg/mm2 (range: 52-66), corresponding to a Mohs hardness of ∼2-3. In reflected light, carducciite is dark grey in colour, moderately bireflectant; internal reflections are very weak and deep red in colour. Reflectance percentages for the four COM wavelengths [R min, Rmax (%) (λ)] are: 35.8, 40.8 (471.1 nm), 33.7, 39.0 (548.3 nm), 32.7, 37.6 (586.6 nm) and 30.4, 35.1 (652.3 nm). Electron microprobe analysis gives (wt.%-mean of six analyses): Ag 3.55(12), Tl 0.13(3), Pb 41.90(42), Sb 17.79(19), As 12.41(14), S 22.10(17), total 97.9(6). On the basis of ∑Me = 16 a.p.f.u., the chemical formula is Ag0.96Tl0.02Pb5.91As4.84Sb4.27S20.14. The main diffraction lines, corresponding to multiple hkl indices, are (relative visual intensity): 3.689 (s), 3.416 (s), 3.125 (s), 2.989 (s), 2.894 (s), 2.753 (vs), 2.250 (s). The crystal-structure study gives a monoclinic unit cell, space group P21/c, with a 8.4909(3), b 8.0227(3), c 25.3957(9) Å, β 100.382(2)°, V 1701.63(11) Å3, Z = 2. The crystal structure has been solved and refined to a final R 1 = 0.063 on the basis of 4137 observed reflections. It can be described within the framework of the sartorite homologous series, as formed by chemically twinned layers of the dufrenoysite type. The simplified idealized structural formula, based on 20 sulfur atoms, can ideally be written as (AgSb)Pb6(As,Sb)∑=8S20. Carducciite is an (Ag,Sb)-rich homeotype of dufrenoysite, stabilized by the complete coupled substitution 2 Pb2+ = Ag+ + Sb3+ on a specific site of the crystal structure. Together with barikaite, it belongs to the rathite sub-group of P 21/c homeotypes of dufrenoysite, of which the crystal chemistry is discussed. The distribution of Ag, coupled with As or Sb on specific sites, appears to be the main criterion for the distinction between the three species of this sub-group
Oyonite, Ag3Mn2Pb4Sb7As4S24, a new member of the lillianite homologous series from the Uchucchacua base-metal deposit, Oyon district, Peru
Full text linkThe new mineral species oyonite, ideally Ag3Mn2Pb4Sb7As4S24, has been discovered in the Uchucchacua base-metal deposit, Oyon district, Catajambo, Lima Department, Peru, as very rare black metallic subhedral to anhedral crystals, up to 100 μm in length, associated with orpiment, tennantite/tetrahedrite, menchettiite, and other unnamed minerals of the system Pb-Ag-Sb-Mn-As-S, in calcite matrix. Its Vickers hardness (VHN100) is 137 kg/mm2(range 132-147). In reflected light, oyonite is weakly to moderately bireflectant and weakly pleochroic from dark grey to a dark green. Internal reflections are absent. Reflectance values for the four COM wavelengths [Rmin, Rmax(%) (λ in nm)] are: 33.9, 40.2 (471.1), 32.5, 38.9 (548.3), 31.6, 38.0 (586.6), and 29.8, 36.5 (652.3). Electron microprobe analysis gave (in wt %, average of 5 spot analyses): Cu 0.76 (2), Ag 8.39 (10), Mn 3.02 (7), Pb 24.70 (25), As 9.54 (12), Sb 28.87 (21), S 24.30 (18), total 99.58 (23). Based on 20 cations per formula unit, the chemical formula of oyonite is Cu0.38Ag2.48Mn1.75Pb3.79Sb7.55As4.05S24.12. The main diffraction lines are (d in Å, hkl and relative intensity): 3.34 (−312, 40), 3.29 (−520, 100), 2.920 (−132, 40), 2.821 (−232, 70), 2.045 (004, 50). The crystal structure study revealed oyonite to be monoclinic, space group P21/n, with unit-cell parameters a = 19.1806 (18), b = 12.7755 (14), c = 8.1789 (10) Å, β = 90.471 (11)°, V = 2004.1 (4) Å3, Z = 2. The crystal structure was refined to a final R1 = 0.032 for 6272 independent reflections. Oyonite belongs to the Sb-rich members of the andorite homeotypic sub-series within the lillianite homologous series. The name oyonite is after the Oyon district, Lima Department, Peru, the district where the type locality (Uchucchacua mine) is located
Ciriottiite, Cu(Cu,Ag)3Pb19(Sb,As)22(As2)S56, the Cu-analogue of sterryite from the Tavagnasco mining district, Piedmont, Italy
Full text linkThe new mineral species ciriottiite, ideally Cu(Cu,Ag)3Pb19(Sb,As)22(As2)S56 has been discovered in the Tavagnasco mining district, Piedmont, Italy, as very rare black metallic tubular crystals, up to 150 μm in length, associated with Bi sulfosalts and arsenopyrite. Its Vickers hardness (VHN10) is 203 kg/mm2 (range 190-219). In reflected light, ciriottiite is light grey in color, distinctly anisotropic with brownish to greenish rotation tints. Internal reflections are absent. Reflectance values for the four COM wavelengths (Rmin, Rmax (%) (λ in nm)) are: 33.2, 37.8 (471.1); 31.8, 35.3 (548.3), 31.0, 34.7 (586.6); and 27.9, 32.5 (652.3). Electron microprobe analysis gave (in wt %, average of 5 spot analyses): Cu 2.33 (8), Ag 0.53 (5), Hg 0.98 (6), Tl 0.78 (3), Pb 44.06 (14), As 4.66 (7), Sb 23.90 (10), Bi 1.75 (7), total 99.38 (26). On the basis of 56 S atoms per formula unit, the chemical formula of ciriottiite is Cu3.23(11)Ag0.43(4)Hg0.43(2)Pb18.74(9)Tl0.34(1)Sb17.30(5)As5.48(10)Bi0.74(3)S56. The main diffraction lines, corresponding to multiple hkl indices, are (d in Å (relative visual intensity)): 4.09 (m), 3.91 (m), 3.63 (vs), 3.57 (m), 3.22 (m), 2.80 (mw), 2.07 (s). The crystal structure study revealed ciriottiite to be monoclinic, space group P21/n, with unit-cell parameters a = 8.178 (2), b = 28.223 (6), c = 42.452 (5) Å, β= 93.55 (2)°, V = 9779.5 (5) Å3, Z = 4. The crystal structure was refined to a final R1 = 0.118 for 21304 observed reflections. Ciriottiite is the Cu analogue of sterryite and can be described as an expanded derivative of owyheeite. The name ciriottiite honors Marco Ernesto Ciriotti (b. 1945) for his longstanding contribution to mineral systematics
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
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