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1.
Résumé L'étude chimique comparée, à la microsonde électronique, d'owyheeite de treize gisements différents a révélé des fluctuations sensibles des teneurs en éléments majeurs, en liaison avec la nature des sulfosels associés, ainsi que la présence occasionnelle de différents éléments mineurs: Cu et As (très fréquents), Sn et Bi (moins fréquents), Tl et Se (exceptionnels). Compte tenu du mode de substitution de ces éléments mineurs, la projection des analyses dans le système Pb2S2–Ag2S–Sb2S3 délimite un champ restreint de solution solide dont l'allongement s'accorde avec la substitution 2 Pb2+Ag++Sb3+. Ce champ de solution solide englobe la composition de la variété téremkovite, mais exclue la formule donnée initialement parShannon. La formule Pb10–2x Sb11+x Ag3+x S28 (–0,13x+0,20) rend compte des termes à la résolution de la Ag/Sb maximal; l'obtention d'une formule plus générale reste subordonée à la résolution de la structure cristalline. Aucun élément mineur ne peut jouer à lui seul le rôle de stabilisateur de la structure, mais ce même rôle peut être joué complémentairement par différents éléments, tels que Cu et Sn. Les clichés de microdiffraction électronique montrent des phénomènes de sur-structure plus ou moins prononcés, en liaison avec la concentration en (Ag+Cu), ou avec le degré de finesse du maclage complexe spécifique de l'owyheeite.
Crystal chemistry of owyheeite: New data
Summary Comparative electron microprobe study of owyheeite from thirteen ore deposits shows significant variations in the concentration of major elements. These can be correlated with the chemical composition of the associated sulfosalts. Sometimes, some minor elements may be present: Cu and As (very frequent), Sn and Bi (less frequent), Tl and Se (exceptional). Considering certain substitution rules for minor elements, the analyses plotted in the Pb2S2–Ag2S–Sb2S3 system show a limited solid-solution field, the elongation of which follows the substitution 2 Pb2+Ag++Sb3+. This solid-solution field includes the composition of the variety teremkovite, but excludes the initial formula for owyheeite proposed byShannon. The formula Pb10–2x Sb11+x Ag3+x S28 (–0.13x+0.20) describes compositional variation of members with the highest Ag/Sb ratio; a more general formula would require the determination of the crystal structure. No individual minor element appears to be responsible for stabilizing owyheeite. The stabilization may be due to a combined effect of two elements, such as Cu and Sn. Electron diffraction patterns show superstructure reflections which are related to the (Ag+Cu) concentration, as well as to the scale of the complex twinning characteristic of owyheeite.

Avec 3 Figures  相似文献   

2.
L-edge X-ray absorption spectroscopy employing a synchrotron radiation source has been used to study the electronic structure and valency of Cu in the chemically and structurally complex tetrahedrite group of minerals. Mechanical mixtures of Cu2+O and Cu+FeS2 were used to estimate the relative cross sections of Cu2+ and Cu+; the absorption of Cu2+ at 931 eV is 25 times greater than that of Cu+ at 945 eV. Using this calibration, Cu2+/Cu ratios were found to vary from 0.00 to 0.054 in the tetrahedrite samples studied; the highest proportion of Cu2+ occurs in synthetic tetrahedrites with a composition close to Cu12Sb4S13. This study reveals the utility of the technique for determining the valence state of copper in complex minerals, allowing the crystal chemistry to be more fully characterised.  相似文献   

3.
Electron microprobe analysis of Pb-Cu(Fe)-Sb-Bi sulfosalts from Bazoges and Les Chalanches (France), and Pedra Luz (Portugal), give new data about (Bi, Sb) solid-solution and incorporation of the minor elements Cu, Fe or Ag in jaskolskiite, and in izoklakeite-giessenite and kobellite-tintinaite series. Jaskolskiite from Pedra Luz has high Sb contents (from 17.9 to 20.7 wt.%), leading to the extended general formula: Cu x Pb2+x (Sb1–y Bi y )2–x S5, with 0.10 x 0.22 and 0.19 y 0.41. Fe-free, Bi-rich izoklakeite from Bazoges has high Ag contents (up to 2.2 wt. %), leading to the simplified formula Cu2Pb22Ag2(Bi, Sb)22S57; in Les Chalanches it contains less Ag content (1.2 wt.%), but has an excess of Cu that gives the formula: Cu2.00 (Cu0.49Ag1.18)=1.67Pb22.70(Bi12.63Sb8.99)=21.62S57.27.In tintinaite from Pedra Luz, the variation of the Fe/Cu ratio can be explained by the substitution: Cu + (Bi, Sb) Fe + Pb; Fe-free kobellite from Les Chalanches has a Cu-excess, corresponding to the formula Cu2.81Ag0.54Pb9.88(Bi10.37Sb5.21)=15.38S35.09. Eclarite from the type locality, structurally related to kobellite, shows a Cu excess too. In natural samples of the kobellite homologous series, Fe is positively correlated with Pb, and its contents never exceed that of Cu. Ag substitutes for Pb, together with (Bi, Sb). Taking into account the possibility of Cu excess, but excluding formal Cu2+ and Fe3+, general formulae can be written:  相似文献   

4.
Tetrahedrites of composition (Cu, Ag)10(Cu2, Fe, Zn)2(Sb, As)4S13 or Cu12Sb14/3S13 have 208 valence electrons per unit cell and are expected to be semiconductors. The bands are full in these cases, whereas compositions towards the classical formula Cu12Sb4S13 (204 valence electrons per unit cell) have only partially filled bands and are therefore expected to be metallic. These predictions are supported by new optical absorption spectra of tetrahedrites with 205 and 208 valence electrons per unit cell. The gap between valence and conduction bands of the semiconductor is about 1.7 (±0.2) eV. A further prediction based on a nearly-free electron model is that 208 valence electrons per unit cell represent a compositional limit for tetrahedrites, and that the stability increases as compositions approach this limit. Existing data indicate an exponential increase in the number of occurrences as the limit is approached.  相似文献   

5.
Zusammenfassung Röntgenographische Untersuchungen an Einkristallen von Arsenbrackebuschit, Pb2(Fe, Zn)(OH, OH2) (AsO4)2 (mit FeZn21), ergaben die RaumgruppeP21/m mita 0=7,763(1) Å,b 0=6.046(1) Å,c 0=9.022(1)Å, =112,5(1)°,V=391,2(1) Å3,Z=2 und x =6,54 g/cm3. Dreidimensionale Fouriersynthesen und Verfeinerungen nach der Methode der kleinsten Quadrate bis zu einemR-Wert von 0,073 zeigten, daß das neue Mineral strukturell einer Gruppe von Blei-Mineralen der allgemeinen Formel Pb2 Me(Z) (XO4) (YO4) — mitMe=Cu2+, Mn2+, Zn2+, Fe3+;X=S, Cr, V, As;Y=P, As, V;Z=OH, OH2 — zuzuordnen ist. Vertreter dieser Gruppe sind z. B. Tsumebit Pb2Cu(OH) (SO4) (PO4), Vauquelinit Pb2Cu(OH) (CrO4) (PO4) und auch Brackebuschit Pb2(Mn, Fe) (OH2) (VO4)2. Strukturelle Verwandtschaft besteht mit Tsumcorit Pb(Zn, Fe)2(OH, OH2)2(AsO4)2, einem weiteren Blei-Arsenat der gleichen Lagerstätte.
Structural investigation of arsenbrackebuschite
Summary X-ray single crystal work on arsenbrackebuschite, Pb2(Fe, Zn) (OH, OH2) (AsO4)2 (with FeZn21), gave space groupP21/m witha 0=7.763(1),b 0=6.046(1),c 0=9.022(1) Å, =112.5(1)°,V=391.2(1) Å3,Z=2 and x =6,54 g/cm3. 3-dimensional Fourier syntheses and least-squares refinement (finalR=0.073) showed that the new mineral belongs to a group of lead minerals with the general formula Pb2 Me(Z) (XO4) (YO4)Me=Cu2+, Mn2+, Zn2+, Fe2+, Fe3+;X=S, Cr, V, As; Y=P, As, V;Z=OH, OH2. Members of this group, are for example tsumebite, Pb2Cu(OH) (SO4)(PO4), vauquelinite, Pb2Cu(OH) (CrO4) (PO4), and brackebuschite, Pb2 (Mn, Fe) (OH2) (VO4)2. A structural relationship exists to tsumcorite, Pb(Zn, Fe)2(OH, OH2)2 (AsO4)2, another lead-arsenate from Tsumeb.

Mit 2 Abbildungen  相似文献   

6.
Summary New compositional and optical data are reported for antimonian and antimonianbismuthian varieties of hemusite from epithermal Au-Ag-Cu deposits in Japan. The empirical formula for the antimonian variety, from the Iriki mine is: (Cu5.83Fe0.14Ag0.01)5.98Mo1.03(Sn0.54Sb0.41Te0.03Bi0.02)1.00(S7.85Se0.15)8.00, and that of the Sb-Bi variety from the Kawazu mine is: (Cu5.84Fe0.14Ag0.01)5.99Mo1.03(Sn0.82Sb0.11Bi0.l0Te0.04)1.07(S7.80Se0.12)7.92. The theoretical formula of hemusite is Cu+ 4Cu2+ 2MO4+Sn4+S8, whilst the most probable formula of the Iriki hemusite is Cu+ 4.5CU2+ 1.5Mo4+Sn4+ 0.5Sb5+ 0.5S8, with Sb5+ substituting for Sn4+ and forming (SbS4)3– tetrahedra as might be expected, given that the metal to sulphur ratio is 1, and given the sphalerite-like structure of the mineral. However Bi3+ cannot be so accommodated, resulting in a deficiency in (S + Se) for Kawazu hemusite. Reflectance spectra for both are compared with those of the tungsten analogue (compositional) of hemusite, kiddcreekite. The relationship between hemusitesensu stricto and these newly reported varieties is discussed in terms of simple and coupled chemical substitutions, and inferences are drawn on the valency of Sb, Bi, Mo and Cu in the hemusite structure.
Neue chemische und optische Daten für antimon- und bismuthführende Varietäten von Hemusit aus Japan
Zusammenfassung Neue chemische und optische Daten für antimon- und bismuthführende Hemusite auf epithermalen Au-Ag-Cu Lagerstätten in Japan werden vorgelegt. Die empirische Formel für die antimon-führende Varietät aus der Iriki-Mine ist: (Cu5.83Fe0.14Ag0.01)5.98Mo1.03(Sn0.54Sb0.41Te0.03Bi0.02)1.00 (S7.85Se0.15)8.00, und die der Sb-Bi Varietät aus der Kawazu Mine ist: (Cu5.84Fe0.14Ag0.01)5.99M01.03(Sn0.82Sb0.11Bi0.l0Te0.04)1.07 (S7.80Se0.12)7.92. Die theoretische Formel von Hemusit ist Cu+ 4Cu2+ 2Mo4+Sn4+S8, während die wahrscheinlichere Formel für den Hemusit von Iriki Cu+ 4Cu2+ 1.5Mo4+Sn4+ 0.5Sb5+ 0.5S8, mit Sb5+ an der Stelle von Sn4+, das(SbS4)3– Tetraeder bildet, wie zu erwarten ist, unter der Voraussetzung, da das Metall zu Schwefelverhältnis 1 und die Struktur sphaleritähnlich ist. Bi3+ kann jedoch nicht in dieser Weise untergebracht werden, und das führt zu einem Mangel an (S + Se) für den Hemusit von Kawazu. Die Reflektions-Spektren beider Minerale werden mit denen des Wolfram-Equivalents von Hemusit (Kiddcreekit) verglichen. Die Beziehung zwischen Hemusitsensu stricto und diesen jetzt beschriebenen Varietäten wird auf der Basis einfacher und gekoppelter chemischer Substitution diskutiert. Auf dieser Basis werden Schlüsse auf die Valenz von Sb, Bi Mo und Cu in der Hemusit-Struktur gezogen.
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7.
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8.
Divariant oxide plus metal assemblages potentially make useful redox sensors for use in hydrothermal and other high pressure experiments. Here we report the calibration of the (Ni, Mn)O/Ni redox sensor in which the Ni/NiO (NNO) oxygen buffer is displaced to lower oxygen chemical potentials (O2), by the solid solution of MnO in the oxide phase. This assemblage was chosen because: (1) it covers a useful range of O2; (2) the system can be calibrated very accurately. Values of O2 defined by the (Ni, Mn)O/Ni assemblage were determined electrochemically, from 900 to 1300 K, using calcia-stabilized zirconia solid electrolytes. The oxide compositions (8 in total, ranging from 0.1X NiO0.8) were analysed afterwards by electron microprobe, and were checked for internal consistency by measuring the lattice parameters (a0), using powder XRD. The accuracies of the measurements, both assessed theoretically and established empirically, are (1): ±80J/mol in O2, ±0.0002 Å in a0 and ±0.002 to 0.005 in X NiO. Activity-composition relations were fitted to the Redlich-Kister formalism. There is a slight asymmetry (corresponding to a subregular model) across the solution with A 0 G =9577(±45) J/mol, and A 1 G =–477(±80) J/mol. The experimental data were also used to derive the parameters Vex, Hex and Sex. There is no obvious relationship between excess volumes and enthalpies of mixing, nor between excess volumes and excess entropies. The experimental data from this study have been used to formulate the (Ni, Mn)O/Ni redox sensor expression: O2 = 2(NNO) + 2RTlnX NiO + 2(1 – X NiO)2[11483 – 1.697T] – 477(4X NiO – 1)(900 < T(K) < 1300) where O2(NNO)=–478967+248.514T–9.7961 T In T, from O'Neill and Pownceby(1993a).  相似文献   

9.
The Hiendelaencina mining district (Guadalajara, Spain), includes the ore deposits of the Hiendelaencina, La Bodera and Congostrina areas. In this paper a general overview of this district is given, with special emphasis on the parageneses, mineralizing stages and chemical characteristics of the sulphides and sulphosalts. These deposits contain silver in Sb-rich sulphosalts such as freibergite, pyrargyrite, polybasite, stephanite, freieslebenite and the Bi-rich sulphosalt, aramayoite. Three mineralizing stages have been detected in Hiendelaencina and Congostrina: (1) As-Fe; (2) Cu-Zn-Fe-Sb-Ag; and (3) Pb-Sb-Ag (±Bi) but only two in La Bodera (stages 2 and 3). The average sulphosalt formulas are: freibergite (Cu0.5 Ag5.9) (Fe1.42 Zn0.66) (Sb4.49 As0.02) S13; pyrargyrite Ag3.38 Sb1.0 S3; polybasite (Ag16.3Cu0.15) (Sb2.8 As0.15) S11; stephanite Ag6.7 Sb1.38 S4; freieslebenite Ag1.1 Sb0.83 Pb1.05 S3 and aramayoite Ag1.06 Bi0. 35 Sb0.7 Pb0.03 S2. The compositional patterns of these sulphosalts (mainly based on the Sb/(Sb + Ag), Ag/ (Ag + Cu), Sb(Ag + As) and Ag/(Ag + Cu) ratios) are outlined, pointing broadly to similar tendencies in their chemistry and genetic conditions.  相似文献   

10.
Iron- and vanadium-bearing kyanites have been synthesized at 900 and 1100° C/20 kb in a piston-cylinder apparatus using Mn2O3/Mn3O4- and MnO/Mn-mixtures, respectively, as oxygen buffers. Solid solubility on the pseudobinary section Al2SiO5-Fe2SiO5(-V2SiO5) of the system Al2O3-Fe2O3(V2O3)-SiO2 extends up to 6.5 mole% (14mole %) of the theoretical end member FeSiO5(V2SiO5) at 900°C/20 kb. For bulk compositions with higher Fe2SiO5 (V2SiO5) contents the corundum type phases M2O3(M = Fe3+, V3+) are found to coexist with the Fe3+(V3+)-saturated kyanite solid solution plus quartz. The extent of solid solubility on the join Al2SiO5-Fe2SiO5 at 1 100°C was not found to be significantly higher than at 900° C. Microprobe analyses of iron bearing kyanites gave no significant indication of ternary solid solubility in these mixed crystals. Lattice constants a 0, b 0, c 0, and V0 of the kyanite solid solutions increase with increasing Fe2SiO5- and V2SiO5-contents proportionally to the ionic radii of Fe3+ and V3+, respectively, the triclinic angles ,, remain constant. Iron kyanites are light yellowish-green, vanadium kyanites are light green. Iron kyanites, (Al1.87 Fe 0.13 3+ )SiO5, were obtained as crystals up to 700 m in length.  相似文献   

11.
Diffusion rates of18O tracer in quartz ( c, 1 Kb H2O) and Amelia albite ( 001, 2 Kb H2O) have been measured, using Secondary Ion Mass Spectrometry (SIMS). A new technique involving hydrothermal deposition of labelled materials has removed the possibility of pressure solution-reprecipitation processes adversely affecting the experiments. Reported diffusion constants are:-quartz ( c), ,Q=98±7 KJ mol–1 (600–825° C, 1 Kb); Amelia albite ( 001), ,Q=85±7 KJ mol–1, (400–600° C, 2 Kb). Measured quartz18O diffusivities decrease discontinuously at the- transition, reflecting strong structural influences. The reported albite data agree with previously recorded studies, but-quartz data indicate significantly lower activation energies. Possible causes of this discrepancy, and some geological consequences, are noted.  相似文献   

12.
Phase relations in the Ag-Fe-S system were determined from 700 to 150 °C by quench experiments with the use of evacuated, sealed, silica tubes as reaction vessels; these data were then used to interpret various aspects of natural occurrences of Ag-Fe-S minerals (e.g. argentiferous pyrite). The assemblages Ag2S+Fe1–x S and Ag2S+FeS2 become stable, with decreasing temperature, at 622±2 ° and 607±2 °C, respectively; their establishments involve ternary invariant conditions. The three condensed phases Ag2S+Fe1–x S+FeS2 become stable together at 532±2 °C through a ternary eutectic reaction near Ag2S in composition. An invariant reaction at 248±8 °C results in the formation of the Ag+FeS2 pair from the Ag2S+Fe7S8 assemblage, which is stable at higher temperatures. The associations of native silver and pyrite are found in certain massive sulfide deposits, whereas natural coexistence of argentite and pyrrhotite has not been documented. Experiments demonstrate the feasibility of retrograde reequilibration in ores to produce the silver+pyrite pair from argentite+pyrrhotite. Less than 0.05 and 0.1 at. % Ag are soluble in FeS2 and Fe1–x S, respectively, at 600 °C and less than 0.8 at. % Fe in Ag2S at 500 °C. Silver does not measurably affect the d 10.2 values of Fe1–x S or the cell dimension of FeS2 (a 25 °C=5.4175±0.0001 Å). This study also demonstrates that at low temperatures the binary fugacity data are applicable to ternary assemblages of the Ag-Fe-S system because of these very limited solubilities. The presence of Fe lowers the fcc bcc inversion temperature of Ag2S more than 50 °C; the exact amount of lowering is dependent on the associated Ag-Fe-S phases. The bcc mono. inversion temperature, however, is not measurably affected. No ternary solid phases were encountered above 150 °C. Heating of sternbergite and argentopyrite (both AgFe2S3) mineral samples shows instability at 152 °C (e.g. partial breakdown of sternbergite in 405 days); rate studies show that a 10 °C temperature increase results in approximately a 5-fold increase in breakdown rate.
Zusammenfassung Für die Interpretation von natürlichen Ag-Fe-S-Mineralen (z. B. silberhaltiger Pyrit) werden die Phasenbeziehungen im System Ag-Fe-S durch quenching Experimente bei Temperaturen von 700 ° bis 150 °C untersucht. Evakuierte und zugeschmolzene Quarzglasröhren dienen dabei als Reaktionsgefäße. Die Phasenassoziationen Ag2S+Fe1–x S (Argentit+Magnetkies) und Ag2S+FeS2 (Argentit+Pyrit) werden mit fallender Temperatur bei 622±2 °C und 607±2 °C stabil. Ihre Bildung ist nur unter ternären, invarianten Bedingungen möglich. Bei 532±2 °C bilden sich durch eutektische Reaktion (nahe der Ag2S-Zusammensetzung) als stabile Phasen Ag2S+Fe1–x S+FeS2. Bei 248±8 °C reagieren Ag2S+Fe7S8, die zwischen Temperaturen von 292 °C bis 248 °C stabil sind, zu Ag+FeS2. Paragenesen von gediegen Silber+Pyrit kommen in einigen massiven Sulfidlagerstätten vor; die Paragenese Argentit+Magnetkies ist dagegen noch nicht beobachtet worden. Die bisherigen experimentellen Ergebnisse machen eine retrograde Wiedereinstellung des Gleichgewichtes von gediegen Silber+Pyrit aus Argentit+Magnetkies wahrscheinlich. Bei 600 °C sind <0,05% bzw. 0,1% Ag in FeS2 und Fe1–x S löslich. Bei 500 °C lösen sich <0,8% Fe in Ag2S. Die Zellkonstanten von Magnetkies (gemessen als d 10,2) und von Pyrit (a 25 °C=5,4175±0,0001 Å) werden durch die Aufnahme von Ag nicht meßbar beeinflußt. Die vorliegenden Ergebnisse zeigen, daß die Fugazitäten bei niederen Temperaturen entlang den binären Schnitten Fe-S und Ag-S auch auf das ternäre System Ag-Fe-S angewendet werden können, weil nur sehr beschränkte Mischbarkeiten existieren. Die Gegenwart von Fe erniedrigt die Inversions-temperatur fcc bcc für Ag2S um mehr als 50 °C. Die genaue Inversions-temperatur wird durch die assozierten Ag-Fe-S Phasen festgelegt. Die bcc mono. Inversionstemperatur wird dagegen nicht meßbar beeinflußt. Oberhalb 150 °C werden keine ternären Phasen beobachtet. Sternbergit und Argentopyrit (beides AgFe2S3-Minerale) werden oberhalb 152 °C instabil (z. B. bricht Sternbergit teilweise nach 405 Tagen zusammen). Eine Temperaturerhöhung um ca. 10 °C erhöht die Zerfallsrate um ein Fünffaches.
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13.
Summary The first Indian occurrence of renierite, [Cu10(Cu0.09Zn0.71Fe0.15)0.15Fe4(Ge1.68V0.03-As0.27)1.98]16.93S16.08 is reported from the Cu-rich basal zone of the polymetallic deposit at Rajpura-Dariba. Optical, X-ray and electron microprobe data on the mineral are compared with those from other occurrences. A slight excess of the iron content compared with the formula Cu10(Zn1–x Cu x )(Ge2–x As x )Fe4S16 ofBernstein (1986) and noticeable differences between Cu-coefficient (in brackets) and As-coefficient are obtained. The substitution scheme in renierite may be more complicated than that suggested byBernstein (1986), and apparently also includes the substitution Cu Zn Fe together with As Ge.
Seltene Minerale von Rajpura-Dariba, India. VII: Renierit
Zusammenfassung Das erste indische Vorkommen von Renierit [Cu10(Cu0.09Zn0.71Fe0.15)0.15Fe4(Ge1.68V0.03As0.27)1.98]16.93S16.08 wird mitgeteilt; dieses liegt in der Kupfer-reichen liegenden Zone der polymetallischen Lagerstätte von Rajpura-Dariba. Optische, Röntgen- und Mikrosondendaten dieses Minerals werden mit solchen von anderen Vorkommen verglichen. Ein leichter Überschuß des Eisengehaltes verglichen mit der Formel Cu10(Zn1–x Cu x )(Ge2–x As x )Fe4S16 vonBernstein (1986) und Unterschiede zwischen dem Cu-Koeffizient (in Klammer) und dem As-Koeffizient wurden festgestellt. Die Art der Substitution in Renierit dürfte komplizierter sein als vonBernstein (1986) vorgeschlagen. Die Substitution Cu Zn Fe zusammen mit As scheint hier eine Rolle zu spielen.

With 4 Figures  相似文献   

14.
Zusammenfassung Mikrosondenanalysen und die Verfeinerung der Kristallstruktur zeigen, daß Sylvanit, AuAgTe4, aus Baia de Arie (=Offenbánya), Rumänien, eine stöchiometrische Zusammensetzung und eine geordnete Kristallstruktur besitzt (a=8,95(1) Å,b=4,478(5) Å,c=14,62(2) Å; =145,35(5)°;Z=2; RaumgruppeP2/c–C 2h 4 ). Das Au-Atom ist von sechs Te-Atomen in einer für die Oxidationszahl III charakteristischen [4+2]-Koordination umgeben. Um das Ag-Atom (Oxidationszahl I) sind ebenfalls sechs Te-Atome, jedoch in einer [2+2+2]-Koordination, angeordnet. Über gemeinsame Kanten bauen AuTe6- und AgTe6-Polyeder Schichten parallel (100) auf. Diese Schichten werden über Te2-Hanteln (Te–Te=2,82 Å) zu einem Gerüst verknüpft.
Crystal chemistry of natural tellurides. I: Refinement of the crystal structure of sylvanite, AuAgTe4
Summary Electron microprobe analyses and the refinement of the crystal structure indicate, that sylvanite, AuAgTe4, from Baia de Arie (=Offenbánya), Romania, has a stoichiometric composition and an ordered crystal structure (a=8.95(1) Å,b=4.478(5) Å,c=14.62(2) Å; =145.35(5)°;Z=2; space groupP2/c–C 2h 4 ). The Au atom is surrounded by six Te atoms in a [4+2] coordination as characteristic for oxidation state III. Around the Ag atom (oxidation state I) are also six Te atoms, but arranged in a [2+2+2] coordination. Via common edges the AuTe6 and AgTe6 polyhedra build up sheets parallel to (100). These sheets are combined to a network of Te2 dumbbells (Te–Te=2.82 Å).

Mit 2 Abbildungen  相似文献   

15.
Evacuated silica tube experiments (+halide flux) were conducted in portions of the system Cu2S-PbS-Sb2S3 at 440°C, using two-pyrrhotite indicator method to measure the sulfur fugacity. Product phases were identified by optical and X-ray powder diffraction methods supplemented with microprobe analyses. In addition to the previously reported mineral phases, famatinite (Cu3SbS4) appears to be a stable phase in the Sb2S3-rich portion of the system. Microprobe data indicate that almost all the sulfosalts depart from stoichiometry. Copper in Pb-Sb sulfosalts and Pb in chalcostibite and skinnerite are indicative of the coupled substitution 2Pb2+=Cu++Sb3+. Pb-solubility in skinnerite and Cu-solubility in zinkenite are dependent on the initial bulk composition of the charges. The compositions of meneghinite and boulangerite compare well with their natural analogues. The maximum isothermal variation of logf s 2 falls in the range of-6.36 (1.06)logf s 211.12 (0.30). The experimentally derived logf s 2 values for some two phase assemblages, compare reasonably well with the respective minimum logf s 2 values calculated by the method of Craig and Barton (1973). The stable coexistence of famatinite with zinkenite plus stibnite instead of chalcostibite may be described by the sulfidation reaction: 3CuSbS2+1/2 S2=Cu3SbS4+Sb2S3.  相似文献   

16.
The assemblage paragonite + quartz is encountered frequently in low- to medium-grade metamorphic rocks. With rising grade of metamorphism they react mutually to yield the condensed assemblage albite + Al2SiO5.The univariant curve pertaining to the equilibrium paragonite + quartz=albite + andalusite + H2O has been located experimentally. The reversed P H 2 O-T data are: 1 kb: 470–490° C 2 kb: 510–530° C 3 kb: 540–560° C 4 kb: 560–580° C 5 kb: 590–600° C The univariant curve pertaining to the equilibrium paragonite + quartz=albite + kyanite + H2O runs through the following P H 2 O-T-intervals: 5 kb: 570–625° C 6 kb: 600–630° C 7 kb: 620–640° C Thermodynamic calculations of S 298 0 , H f,298 0 and G f,298 0 of the phase paragonite from the experimental data presented above and those obtained from the equilibria of the reaction paragonite=albite + corundum + H2O (Chatterjee, 1970), agree within the limits of uncertainty. This prompts the idea that Zen's (1969) suggestion of a possible error of approximately 7 kcal in G f,298 0 of the Al2SiO5 polymorphs may in fact be due to an error of similar magnitude in G f,298 0 of corundum.A best estimate of S 298 0 , H f,298 0 and G f,298 0 of paragonite based on these considerations yield: S 298 0 : 67.61±3.9 cal deg–1 gfw–1 H f,298 0 : –1411.4±2.7 kcal gfw–1 G f,298 0 : –1320.9±4.0 kcal gfw–1 These numbers will be subject to change when better thermochemical data on corundum and albite are available.In medium-grade metamorphic rocks the assemblage paragonite + quartz is commonly found in stable coexistence with such other phases as muscovite, staurolite, andalusite, kyanite, but not with cordierite or sillimanite. However, the assemblage paragonite-sillimanite has been reported to be stable in the absence of quartz. All these petrologic observations can be explained on the basis of the stability data of the phases and phase assemblages concerned.  相似文献   

17.
Zusammenfassung 1Tc-Strontiohilgardit (Ca, Sr)2 [B5O8(OH)2,Cl] mit Ca : Sr etwa 1 : 1 ist ein neues Mineral der Hilgarditgruppe. Fundpunkt: Reyersbausen (9° 59,7 E, 51° 36,6 N), Grube Königshall-Hindenburg, Flöz Staßfurt in sylvinitischer Ausbildung.Konstanten : triklin-pedial,a 0=6,38 Å,b 0=6,480 Å,c 0=6,608 Å, =75,4°,=61,2°, =60,5°; tafelige-gestreckte Links- und Re chtskristalle, farblos, wasserunlöslich, piezoelektrisch. Härte 5–7, Dichte 2,99 g cm–3;n =1,638,n =1,639,n =1,670; 2V =19°.Neue Daten für die Hilgarditgruppe : 2 M (Cc)-Calciumhilgardit (=Hilgardit) =4 Ca2[B5O3(OH)2Cl], Raumgruppe Cc.3Tc-Calciumhilgardit (=Parahilgardit) = 3 Ca2[B5O3(OH)2Cl]; trinklin-pedial, 0=6,31 Å,b =6,484 Å,c 0=17,50 Å; =84,0°,=79,6°, =60,9°.Die Polymorphiebeziehungen sind geometrisch deutbar durch eine spezielle Art der Polytropie (Stapelung von Links- und Rechtskristallen im Elementarbereich).  相似文献   

18.
The role of Fe2+ and Fe3+ in synthetic Fe-substituted tetrahedrite   总被引：3，自引：0，他引：3  
Summary Tetrahedrites with the composition between Cu12Sb4S13 and Cu10Fe2Sb4S13 were synthesized at 457 °C and 500 °C from the elements and carefully studied by Mössbauer spectroscopy of57Fe. Between Cu12Sb4S13 and Cu11Fe1Sb4S13 iron is predominantly ferric. Between Cu11Fe1Sb4S13 and Cu10Fe2Sb4S13 iron is predominantly ferrous and occupies the tetrahedral M1-sites.
Zusammenfassung Die Rolle von Fe2+ und Fe3+ in synthetischen Tetraedriten mit Fe-Substitution Tetraedrite mit einer Zusammensetzung zwischen Cu12Sb4S13 and Cu10Fe2Sb4S13 wurden bei 457 °C und 500 °C aus den Elementen synthetisiert und sorgfdltig mit Mössbauer-Spektroskopie von57Fe untersucht. Zwischen Cu12Sb4S13 and Cu11Fe1Sb4S13 ist Eisen überwiegend dreiwertig. Zwischen Cu11Fe1Sb4S13 and Cu11Fe2Sb4S13 ist Eisen überwiegend zweiwertig und besetzt die tetraedrisch koordinierten M1-Plätze.
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19.
Dalradian metamorphic rocks, Lower Ordovician meta-igneous rocks (MGS) and Caledonian granites of the Connemara complex in SW Connemara all show intense retrograde alteration. Alteration primarily involves sericitization and saussuritization of plagioclase, the alteration of biotite and hornblende to chlorite and the formation of secondary epidote. The alteration is associated with sealed microcracks in all rocks and planes of secondary fluid inclusions in quartz where it occurs, and was the result of a phase of fluid influx into these rocks. In hand specimen K-feldspar becomes progressively reddened with increasing alteration. Mineralogical alteration in the MGS and Caledonian granites took place at temperatures 275±15°C and in the MGS Pfluid is estimated to be 1.5 kbar during alteration. The °D values of alteration phases are:-18 to-29 (fluid inclusions),-47 to-61 (chlorites) and-11 to-31 (epidotes). Chlorite 18O values are +0.2 to +4.3, while 18O values for quartz-K-feldspar pairs show both positively sloped (MGS) and highly unusual negatively sloped (Caledonian granites) arrays, diverging from the normal magmatic field on a - plot. The stable isotope data show that the fluid that caused retrogression continued to be present in most rocks until temperatures fell to 200–140°C. The retrograde fluid had D -20 to-30 in all lithologies, but the fluid 18O varied both spatially and temporally within the range-4 to +7. The fO2 of the fluid that deposited the epidotes in the MGS varied with its 18O value, with the most 18O-depleted fluid being the most oxidizing. The D values, together with low (<0) 18O values for the retrograde fluid in some lithologies indicate that this fluid was of meteoric origin. This meteoric fluid was probably responsible for the alteration in all lithologies during a single phase of fluid infiltration. The variation in retrograde fluid 18O values is attributed to the effects of variable oxygen isotope shifting of this meteoric fluid by fluid-rock interaction. Infiltration of meteoric fluid into this area was most likely accomplished by convection of pore fluids around the heat anomaly of the Galway granite soon after intrusion at 400 Ma. However convective circulation of meteoric water and mineralogical alteration could possible have occurred considerably later.  相似文献   

20.
In contrast to Ferry (1980) (X Ca)-values in garnet even lower than 0.1 have a significant effect on the calculated equilibrium temperature using the experimental calibration of the Fe and Mg paritioning between garnet and biotite. Garnet compositions and Mg/Fe — distribution coefficients from samples of the Eoalpine staurolite — in zone in the southern Ötztal are related by the quadratic regression equation: InK D= -1.7500 (±0.0226) + 2.978 (±0.5317)X Ca Gt -5.906(±2.359)(X Ca Gt )2 Temperatures derived by the Ferry and Spear (1978) calibration using chemistry — correctedK D values are petrologically realistic.Analysis of our data supports non ideal mixing of grossular with almandine — pyrope solid solution. The derived excess mixing energies are quite small for the almandine — pyrope solution (W FeMg= –133 cal/mole) and about +2775 cal/mole for the difference between pyrope-grossular and almandine-grossular solutions (W MgCa —W FeCa) at metamorphic conditions of 570° C and 5,000 bar. The mixing parameters proposed by Ganguly and Saxena (1984) are not confirmed by our data as they would result in significantly lower temperatures.  相似文献   

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