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1.
X-ray absorption spectroscopy using synchrotron radiation has been applied to the investigation of the coordination geometries around Y, Zr and Nb atoms in metamict zircon, gadolinite, fergusonite, euxenite and samarskite. EXAFS and XANES spectra of their crystalline counterparts and synthetic compounds including ZrO2, Y2O3, YNbTiO6, YNbO4, LiNbO3, and NiNb2O6 were also measured for comparison. Metamict zircon shows a significant decrease in its Zr-O bond distances accompanying an increase in distortion of the Zr-O coordination polyhedra as compared with crystalline zircon. On the contrary, the average Nb-O bond distances and the symmetry of the coordination polyhedra around the Nb atoms in metamict euxenite and samarskite resemble those in the crystalline euxenite. Compared with crystalline fergusonite, a decrease in the distortion of the Nb-O octahedra is observed in metamict fergusonite. The structures of the second nearest neighbors (the metal-metal interactions) are largely disrupted in the metamict specimens except for metamict zircon and samarskite with high trivalent iron concentration. Nb in metamict samarskite is in octahedral coordination by oxygen and is similar to that in euxenite.  相似文献   

2.
Ti site occupancy in zircon   总被引：1，自引：0，他引：1  
Ti site occupancy in zircon (ZrSiO4) is fundamental to thermobarometry because substitution mechanisms control Ti content-temperature relations. Here we describe the results of three independent methods used to demonstrate that Ti substitutes for Si and not Zr in zircon. Zircon grains were synthesized from oxide powders held in a Na2WO4 flux at 1 bar and 1300 °C. Zircon grains equilibrated with rutile + cristobalite show Ti contents (1201 ppm) nearly half that of zircon grains equilibrated with srilankite ((Ti,Zr)O2) + tetragonal zirconia (2640 ppm). The lower Ti content of zircon grains produced at silica-saturated conditions indicates that Ti substitution predominately occurs on the Si site. Moreover, the higher Ti contents of silica-saturated experiments at 1 bar (1201 ppm), relative to those at 1 GPa (457 ppm, Ferry and Watson, 2007), indicates a substantial pressure effect on Ti solubility in zircon. Measured Ti K-α edge X-ray Absorption Near Edge Structure (XANES) spectra of synthetic zircon grains show energies and normalized intensities akin to those seen among tetrahedrally coordinated Ti-bearing standard minerals, strongly suggesting that Ti occupies the Si site. Density functional theory (DFT) calculations confirm that Ti substitution is most likely to occur on the Si site and predict a Ti-O bond length of 1.797 Å (compared to an average of 2.160 Å for substitution on the Zr site), in excellent agreement with X-ray Absorption Fine Structure (EXAFS) spectra of experimentally grown zircon grains which indicate a value of 1.76(1) Å. The software FEFF 8.4 was used to simulate XANES spectra from the defect structures determined by DFT for Ti substituting on both the Si and Zr sites. The predicted spectrum for Ti on the Si site reproduces all the key features of the experimental zircon spectra, whereas Ti on the Zr site is markedly different. All applied methods confirm that Ti substitutes for Si in zircon. Consequently, the Ti content of zircon at a given pressure is not only a function of temperature, but will increase with decreasing silica activity. Because elements that activate or quench cathodoluminescence (CL) in zircon are incorporated into the Zr site, a decoupling of CL from Ti contents - incorporated on the Si site in zircon is expected. This hypothesis has been verified by a systematic CL-trace element study of natural and experimental zircon.  相似文献   

3.
Crystallization thermometers for zircon and rutile   总被引：93，自引：20，他引：73  
Zircon and rutile are common accessory minerals whose essential structural constituents, Zr, Ti, and Si can replace one another to a limited extent. Here we present the combined results of high pressure–temperature experiments and analyses of natural zircons and rutile crystals that reveal systematic changes with temperature in the uptake of Ti in zircon and Zr in rutile. Detailed calibrations of the temperature dependencies are presented as two geothermometers—Ti content of zircon and Zr content of rutile—that may find wide application in crustal petrology. Synthetic zircons were crystallized in the presence of rutile at 1–2 GPa and 1,025–1,450°C from both silicate melts and hydrothermal solutions, and the resulting crystals were analyzed for Ti by electron microprobe (EMP). To augment and extend the experimental results, zircons hosted by five natural rocks of well-constrained but diverse origin (0.7–3 GPa; 580–1,070°C) were analyzed for Ti, in most cases by ion microprobe (IMP). The combined experimental and natural results define a log-linear dependence of equilibrium Ti content (expressed in ppm by weight) upon reciprocal temperature:
In a strategy similar to that used for zircon, rutile crystals were grown in the presence of zircon and quartz (or hydrous silicic melt) at 1–1.4 GPa and 675–1,450°C and analyzed for Zr by EMP. The experimental results were complemented by EMP analyses of rutile grains from six natural rocks of diverse origin spanning 0.35–3 GPa and 470–1,070°C. The concentration of Zr (ppm by weight) in the synthetic and natural rutiles also varies in log-linear fashion with T −1:
The zircon and rutile calibrations are consistent with one another across both the synthetic and natural samples, and are relatively insensitive to changes in pressure, particularly in the case of Ti in zircon. Applied to natural zircons and rutiles of unknown provenance and/or growth conditions, the thermometers have the potential to return temperatures with an estimated uncertainty of ±10 ° or better in the case of zircon and ±20° or better in the case of rutile over most of the temperature range of interest (∼400–1,000°C). Estimates of relative temperature or changes in temperature (e.g., from zoning profiles in a single mineral grain) made with these thermometers are subject to analytical uncertainty only, which can be better than ±5° depending on Ti or Zr concentration (i.e., temperature), and also upon the analytical instrument (e.g., IMP or EMP) and operating conditions.  相似文献   

4.
Electron backscatter imaging, Raman spectroscopy and U-Pb geochronology have been applied to Precambrian zircon grains that were annealed at 1000 and 1450 °C for various times, then leached with HF to constrain the conditions for healing radiation damage and attaining primary U-Pb zircon ages using the chemical abrasion (CA-TIMS) method. SEM images reveal a variety of textures for ZrO2 overgrowths on 1450 °C annealed and leached zircon surfaces that depend on the degree of radiation damage and annealing history. Highly damaged zircon produces finer textures than zircon with less damage.Raman spectroscopy indicates that crystals with different levels of radiation damage are only partially restored by annealing at 1000 °C for 2-3 days. Longer annealing periods of 20 days are not noticeably more effective. Annealing at 1450 °C for 1 h results in partial breakdown of zircon but restores Raman peak widths and wave numbers to values characteristic of undamaged zircon after ZrO2 overgrowths are removed by HF. Raman spectra are much less sensitive to polarization angle for annealed highly damaged grains than for weakly damaged zircon.U-Pb isotopic analyses of low to moderately damaged zircon (alpha fluence ranging up to 1019/g corresponding to an amorphization volume fraction of 80% or more) yield almost concordant data (0.3-0.5% discordance) after high-temperature annealing at 1450 °C followed by HF leaching at 195 °C. Analyses of cracked zircon annealed at 1450 °C and leached may remain discordant but those of uncracked grains are concordant. Most analyses show primary 207Pb/206Pb ages although cracked grains annealed at 1450 °C may produce discordant data with 207Pb/206Pb ages that are too young after leaching. The solubility of highly damaged, very disordered zircon (amorphization level of 99%) is only slightly reduced by annealing, and analyses of leach residues are strongly discordant although primary 207Pb/206Pb ages are obtained.Annealing of highly damaged zircon under any conditions apparently results in a mass of randomly oriented micro-crystals that pseudomorph the original grain. This could explain the fine-scale pattern observed on etched crystal surfaces, reduced anisotropy at the 5 μm scale of the Raman laser beam and high solubility in HF. It may be impossible to restore primary U-Pb isotopic ages in such cases but precise ages can still potentially be determined from 207Pb/206Pb ratios or by application of the air abrasion method.  相似文献   

5.
Al-Si ordering in Sr-feldspar has been followed by isothermal annealing, starting from a disordered metastable configuration. Ordering could not be followed by changes in the spontaneous strain as cell parameters did not show significant changes with thermal treatment from 0.016 h to 452 h at T=1350° C, while, on the contrary, significant changes in IR spectra are observed. A single crystal obtained from melt (Q od 0) has been progressively heated up to 678 h at T=1350° C and the relevant structural refinements enabled to monitor changes in degree of Al-Si order up to Qod = 0.86. In isothermal treatment for Sr-feldspar it is observed a significantly lower Q od than in anorthite after the same annealing time. TEM observation has shown in Sr-feldspar, also for shortest annealing, b type reflections, while in anorthite, in the same conditions, e type reflections have been observed (Carpenter 1991a). In the first stages of ordering b APDs sized 100 Å (at T=1350° C, 0.33 h) have been observed in Sr-feldspar; APD coarsening occurs with an activation energy of 120±7 kcal mol-1, not significantly different from anorthite. The ordering process seems to be a slower process in Sr-feldspar than in anorthite, even though data from longer annealing suggest that the Q od close to the equilibrium is the same in Sr and Ca-feldspar (Q od = 0.86 at T=1350° C).  相似文献   

6.
Summary The crystal structure of hydrothermally grown NaFe[SeO4]2 was determined by single crystal X-ray diffraction methods: space group C2/m, a = 8.231(1)Å b = 5.425(1)Å, c = 7.176(1)Å, = 92.44(1)°, V = 320.14Å3, Z = 2; 767 unique data, measured up to 20 = 70° (Mo Kx radiation); R,RW= 0.042, 0.055.NaFe[SeO4]2 is isotypic with yavapaiite, KFe[SO4]2. FeO6 and NaO6 form chains of edge-sharing distorted octahedra with mean Me-O bond lengths of 2.001Å and 2.496Å, respectively, linked via tetrahedral SeO4 groups [
Die Kristallstruktur von NaFe[SeO4]2, einer Verbindung des Yavapaiit-Typsre]19921030
Zusammenfassung Die Kristallstruktur von hydrothermal gezüchtetem NaFe[SeO4]2 wurde mittels Einkristallröntgenmethoden bestimmt: Raumgruppe C2/m, a = 8.231(1)Å, b = 5.425(1)Å, c = 7.176(1)Å, = 92.44(1)°, V = 320.14Å3, Z = 2; 767 unabhängige Intensitätsdaten, Meßbereich bis 20 = 70° (Mo K-Strahlung); R,RW = 0.042, 0.055.NaFe[SeO4]2 ist isotyp mit Yavapaiit, KFe[SO4]2. FeO6 und NaO6 bilden Ketten von kantenverknüpften, verzerrten Oktaedern mit mittleren Me-O Bindungslängen von 2.001Å bzw. 2.496Å, die über tetraedrische SeO4 Gruppen verbunden sind [ = 1.639Å].

Dedicated to Prof. Josef Zemann on the occasion of his 70th birthday

With 3 Figures  相似文献   

7.
The polymorphic transformation between synthetic pyroxmangite and rhodonite of MnSiO3 composition has been reversibly bracketed in the presence of water at 3 kbar (between 425 ° and 450 ° C), 6 kbar (between 475 ° and 525 ° C), 20 kbar (between 500 ° and 900 ° C), 25 kbar (between 800 ° and 900 ° C) and 30 kbar (between 900 ° and 1,000 ° C), using standard cold-seal pressure vessels and piston cylinder apparatus. Oxygen fugacities buffered by the bomb walls and piston-cylinder cell assemblies sufficed to keep manganese in the divalent state. Pyroxmangite of MnSiO3 composition is shown to be the high-pressure, low-temperature polymorph with respect to rhodonite of the same composition. It is a stable phase at atmospheric pressure below 350–405 ° C.X-ray data for synthetic pyroxmangite are presented. The unit-cell parameters (a0=6.717(2) Å, b0=7.603(1)Å, c0=17.448(5) Å, =113 °50(1), = 82 °21(2), =94 °43(1); space group P-1) give a unit-cell volume (807.5(0.3) Å3) which, in accordance with other recent least squares lattice refinements of hydrothermally synthesized material, is slightly smaller than that obtained by single-crystal work on anhydrously synthesized material.Application of the present results to natural rocks is severely restricted due to the great variety and extent of cationic substitutions observed in natural pyroxenoids. The univariant polymorphic transformation determined for the MnSiO3 composition is thus replaced in natural systems by a divariant field in which pyroxmangite and rhodonite of differing composition will stably coexist.  相似文献   

8.
Rutile is an important carrier of high field strength elements (HFSE; Zr, Nb, Mo, Sn, Sb, Hf, Ta, W). Its Zr content is buffered in systems with quartz and zircon as coexisting phases. The effects of temperature (T) and pressure (P) on the Zr content in rutile have been empirically calibrated in this study by analysing rutile–quartz–zircon assemblages of 31 metamorphic rocks spanning a T range from 430 to 1,100°C. Electron microprobe measurements show that Zr concentrations in rutile vary from 30 to 8,400 ppm across this temperature interval, correlating closely with metamorphic grade. The following thermometer has been formulated based on the maximum Zr contents of rutile included in garnet and pyroxene:
No pressure dependence was observed. An uncertainty in absolute T of ±50°C is inherited from T estimates of the natural samples used. A close approach to equilibrium of Zr distribution between zircon and rutile is suggested based on the high degree of reproducability of Zr contents in rutiles from different rock types from the same locality. At a given locality, the calculated range in T is mostly ±10°C, indicating the geological and analytical precision of the rutile thermometer. Possible applications of this new geothermometer are discussed covering the fields of ultrahigh temperature (UHT) granulites, sedimentary provenance studies and metamorphic field gradients.  相似文献   

9.
A pink-colored (HUE 5R-7/4), predominantly calcium saturated, clay mineral from Tirebolu, NE-Turkey, is shown to be a dioctahedral, high-charge manganiferous smectite. It is probably an alteration product of volcanic tuffs of rhyodactitic composition. Ionic formula: (Si7.71Al0.29)IV(Al3.04Fe 0.12 3+ Fe 0.02 2+ Mg0.92Mn 0.07 2+ )VI O20 (OH)4 0.79 M+ Cation exchange capacity: 92 me/100 g (air dry sample). Unit cell parameters (ca. 20 ° C; ca. 40% RH): a09.02 Å b05.21 Å Mg++... Mn-smectite: c014.65 Å Ca++... Mn-smectite: c014.83 Å K+... Mn-smectite: c012.10 Å
Zusammenfassung Ein rosa (HUE 5R-7/4), weitgehend Calcium-gesättigtes Tonmineral von Tirebolu (NO-Türkei) wurde als ein dioktaedrischer, hochgeladener manganhaltiger Smektit identifiziert. Er ist wahrscheinlich ein Umwandlungsprodukt eines rhyodazitischen Tuffs. Strukturformel: (Si7.71Al0.29)IV(Al3.04Fe 0.12 3+ Fe 0.02 2+ Mg0.92Mn 0.07 2+ )VI O20 (OH)4 0.79 M+ Kationaustauschkapazität: 92 me/100 g (luftgetrocknet). Gitterkonstanten (ca. 20° C; ca. 40% RF): a09.02 Å b05.21 Å Mg++... Mn-Smektit: c014.65 Å Ca++... Mn-Smektit: c014.83 Å K+... Mn-Smektit: c012.10 Å
  相似文献   

10.
Hydrothermal experiments were carried out at 2 kbar water pressure, 700 °–800 ° C, with the objective of determining the level of dissolved Zr required for precipitation of zircon from melts in the system SiO2-Al2O3-Na2O-K2O. The saturation level depends strongly upon molar (Na2O + K2O)/Al2O3 of the melts, with remarkably little sensitivity to temperature, SiO2 concentration, or melt Na2O/ K2O. For peraluminous melts and melts lying in the quartz-orthoclase-albite composition plane, less than 100 ppm Zr is required for zircon saturation. In peralkaline melts, however, zircon solubility shows pronounced, apparently linear, dependence upon (Na2O + K2O)/Al2O3, with the amount of dissolvable Zr ranging up to 3.9 wt.% at (Na2O + K2O)/Al2O3 = 2.0. Small amounts (1 wt.% each) of dissolved CaO and Fe2O3 cause a 25% relative reduction of zircon solubility in peralkaline melts.The main conclusion regarding zirconium/zircon behavior in nature is that any felsic, non-peralkaline magma is likely to contain zircon crystals, because the saturation level is so low for these compositions. Zircon fractionation, and its consequences to REE, Th, and Ta abundances must, therefore, be considered in modelling the evolution of these magmas. Partial melting in any region of the Earth's crust that contains more than 100 ppm Zr will produce granitic magmas whose Zr contents are buffered at constant low (< 100 ppm) values; unmelted zircon in the residual rock of such a melting event will impart to the residue a characteristic U- or V-shaped REE abundance pattern. In peralkaline, felsic magmas such as those that form pantellerites and comendites, extreme Zr (and REE, Ta) enrichment is possible because the feldspar fractionation that produces these magmas from non-peralkaline predecessors does not drive the melt toward saturation in zircon.Zircon solubility in felsic melts appears to be controlled by the formation of alkali-zirconosilicate complexes of simple (2:1) alkali oxide: ZrO2 stoichiometry.  相似文献   

11.
Summary The mixed valent iron silicate ilvaite CaFe 2 2 +Fe3+ [Si2O7/O/(OH)] has been synthesized under hydrothermal conditions at temperatures between 300 and 500°C, pressures between 1.5 and 4 Kbars and oxygen fugacities controlled by the solid state buffers Fe3O4/Fe2O3, Fe/Fe3O4 and Ni/NiO. All these ilvaites are monoclinic (P21/a with cell parameters a0 = 13.0065 (9) Å, b0 = 8.8073 (7) Å, c0 = 5.8580 (4) Å, and = 90.332 (6)°. The quality of the samples has been checked by Mössbauer spectroscopy. Scanning electron microscopic pictures show small euhedral crystals with a size up to 30 .
Synthese und Charakterisierung des gemischt valenten Eisensilikates Ilvait, CaFe3 [Si2O7/ 0/(OH)]
Zusammenfassung Das gemischt valente Eisensilikat Ilvait CaFe 2 2 +Fe3+ [Si2O7/0/(OH)] wurde unter hydrothermalen Bedingungen bei Temperaturen zwischen 300 und 500 °C, Drucken zwischen 1,5 und 4,0 Kbar und bei Sauerstoff-Fugazitäten, die durch Festkörperpuffer (Fe3O4/Fe2O3, Fe/Fe3O4 and Ni/NiO) kontrolliert wurden, hergestellt. Diese Ilvaite sind alle monoklin mit den Zellparameters a0=13,0065 (9) Å, b0 = 8,8073 (7) Å, c0 = 5,8580 (4) Å und = 90,332 (6)°. Die Qualität der Proben wurde mit Mössbauer Spektroskopie überprüft. Rasterelektronenmikroskopische Aufnahmen zeigten idiomorphe Kristalle mit einer Größe bis 30 .

With 6 Figures  相似文献   

12.
Summary Referring to the natural formation of secondary uranium minerals, the primary transformation of U3O8 into schoepite has been investigated. The transformation is realized in a continuous system with O2, CO2 and H2O. At 100°C schoepite III, UO3 · zH2O (z 1), is formed (a = 14.12; b = 16.83; c = 15.22 Å) with a density of 4.460 g/cm3. At 25°C a mixture of schoepite II (UO3 · yH2O, 1 < y < 2; a = 13.99; b = 16.72; c = 14.73 Å) and schoepite I (UO3 · xH2O, x 2; a = 14.33; b = 16.79; c = 14.73 Å) is obatined. From thermogravimetric analysis the activation energy of dehydration for schoepite III is determined as 49(3) · 103 J/mole.
Umwandlung von synthetischem U3O8 in verschiedene Uranoxidhydrate
Zusammenfassung In Hinblick auf die natürliche Bildung sekundärer Uranminerale wurde die primäre Umwandlung von U3O8 in Schoepit untersucht. Die Umwandlung wurde in einem kontinuierlichen System mit O2, CO2 und H2O bewerkstelligt. Bei 100°C bildet sich Schoepit III (UO3 · zH2O, z 1; a = 14.12, b = 16.83, c = 15.22 Å; Dichte: 4.460 g/cm3). Bei 25°C wird eine Mischung von Schoepit II (UO3 · yH2O, 1 < y < 2; a = 13.99, b = 16.72, c = 14.73 Å) und Schoepit I (UO3 · xH2O, x 2; a = 14.33, b = 16.79, c = 14.73 Å) erhalten. Aus der thermogravimetrischen Analyse wurde die Aktivierungsenergie der Dehydratation von Schoepit III mit 49(3) · 103 J/mole berechnet.

Who wishes to dedicate the paper to the memory of his father, Hendrik Vochten.

With 3 Figures  相似文献   

13.
Giester  G. 《Mineralogy and Petrology》1995,53(1-3):165-171
Summary The crystal structure of synthetic KMn[SeO4]2 was determined by single crystal X-ray diffraction methods in space group , a = 4.827(2) Å, b = 4.988(2) Å, c = 7.981(3) Å, = 83.18(1)°, = 85.32(2)°, = 67.92(1)°, V = 176.66 Å3, Z = 1; 1564 unique data, measured up to 2 = 70° (MoK-radiation); R, R(I)w = 0.034, 0.074.KMn[SeO4]2 is closely related to monoclinic yavapaiite, KFe[SO4]2, and isotypic compounds. Jahn-Teller distorted MnO6 octahedra are alternately linked with KO10 polyhedra along [001]. The mean values of the Mn-O and Se-O distances are 2.007 Å and 1.637 Å, respectively.
Die Kristallstruktur vonKMn 3+[SeO4]-einem triklin verzerrten Vertreter der Yavapaiite-Familie
Zusammenfassung Die Kristallstruktur von synthetisch dargestelltem KMn[SeO4]2 wurde mittels Einkristallröntgenmethoden in der Raumgruppe bestimmt: a = 4.827(2) Å, b = 4.988(2) Å, c = 7.981(3) Å, = 83.18(1)°, = 85.32(2)°, = 67.92(1)°, V = 176.66 Å3, Z = 1; 1564 unabhängige Daten bis 2 = 70° (MoK-Strahlung); R, R(I)w = 0.034, 0.074.KMn[SeO4]2 ist eng mit dem monoklinen Mineral Yavapaiit, KFe[SO4]2 und einer Reihe damit isotyper Verbindungen verwandt. Jahn-Teller verzerrte MnO6 Oktaeder sind alternierend mit KO10 Polyedern parallel [001] verbunden. Die Mittelwerte der Mn-O und Se-O Abstände sind 2.007 Å bzw. 1.637 Å.

With 1 Figure  相似文献   

14.
Zusammenfassung Rooseveltit findet sich in der Oxidationszone der Lagerstätten San Francisco de los Andes und Cerro Negro de la Aguadita, in der Provinz San Juan, Argentinien, auf 30°22 S und 69°33 W. Er bildet sehr feinkörnige, weiß-graue, nach Bismuthinit pseudomorphe Aggregate. Die Brechungsindizes liegen zwischenn=2,10 und 2,30. Die Vickershärte beträgt 513 (4–5 der Mohs'schen Härteskala). Mittels Elektronenmikrosonde wurde folgende chemische Zusammensetzung bestimmt: As=21,5±1%, Bi=60,9±2%. Rooseveltit ist monoklin mita 0=6,878(1)Å, b0=7,163(1) Å, c0=6,735(1) Å, =104° 46±1, Z=4, calc.=6,94 g·cm–3, RaumgruppeP 21/n.Rooseveltit wurde nach drei verschiedenen Methoden synthetisiert. Die Pulverdiagramme der synthetischen Produkte stimmen mit dem des Minerals überein. Die Brechungsindizes wurden mitn =2,13(2) bzw. n=2,25(2) und die Dichte mit obs.=7,01 g·cm–3 bestimmt. Zellparameter: a0-6,882(1) Å, b0=7,164(1) Å, c0=6,734(1) Å, =104° 50,5±0,7, calc.=6,94 g·cm–3. Das synthetische Material schmilzt um 950°C. Selbst nach mehrstündigem Erhitzen auf 920°C läßt sich keine Veränderung im Pulverdiagramm des Minerals festellen.Es wird versucht, die natürliche Bildung des Rooseveltits zu erklären.
Rooseveltite from San Francisco de los Andes and Cerro Negro de la Aguadita, San Juan, Argentina
Summary Rooseveltite occurs in the weathering zone of the San Francisco de los Andes and Cerro Negro de la Aguadita mines, located in the San Juan Province, Argentina, at 30° 22S and 69° 33W. It appears in grey, finegrained aggregates pseudomorph after bismuthinite. Refraction index ranges fromn=2.10 to 2.30. The Vickers microhardness is 513 (4–5 of Mohs' scale). Chemical composition from electron micro probe measurements is As 21.5±1% and Bi 60.9±2%. Rooseveltite is monoclinic, with a0=6.878(1) Å, b0=7.163(1) Å, c0=6.735(1) Å, =104° 46±1, Z=4, calc.=6,94 g·cm–3, space groupP 21/n.The synthetic compound was prepared by three different methods. The powder pattern are the same as that of the mineral. Refraction index n=2.13(2) and n=2.25(2). The measured specific gravity is pobs.=7,01 g·cm–3. Cell parameters: a0=6.882(1) Å, b0=7.164(1) Å,c 0=6.734(1) Å, =104° 50.5±0.7, calc.=6,94 g·cm–3. The synthetic material melts at about 950°C. After heating to 920°C no variations were observed in the powder diagram of the mineral.It is tried to explain the formation of rooseveltite in natural environment.

Mit 2 Abbildungen  相似文献   

15.
Flux-grown crystals of Mg-cordierite, Mg1.93 Al3.95 Si5.07 O18 synthesized by Lee and Pentecost (1976) appear biaxial (2V x=10°–25°) under the polarizing microscope whereas their distortion index =0°. Between crossed polars, (001) sections display lamellar and cyclic twinning on {110} and, less frequently, {310}. As duration of annealing at 1,300° C, increased, 2V x increased. Simultaneously, undulatory extinction and intragrain variations in 2V x increased slightly up to 4 h annealing, then steadily decreased. For this Mg-cordierite, which lacks significant channel H2O or CO2, 2V x and reach maxima of 88° (=589 nm) and 0.25° after 42 h of annealing but other sectors still display lesser values for 2V x. Presumably, to the extent 2V x is less than 88°, these sectors represent intergrown submicros copically twinned orthorhombic domains and thus possess shortrange but not long-range order. Annealing at 1,300° C likely increased long-range order by promoting growth of larger domains at the expense of smaller ones. Ultimately, two differently oriented domains, growing toward each other by annexation (and re-orientation) of smaller domains, meet in a twin boundary that, with time, tends to become straight.The cause of intermediate values for , whether compositional or from submicroscopic {110} or {310} twinning, may be revealed by single crystal X-ray photographs. Streaking of diffraction spots along a* or b* (but not c*) will indicate such twinning as the sole or major cause.  相似文献   

16.
Inhalt Die röntgenographisch bestimmten Daten an einem bergfrischen Laumontit mit etwas mehr als drei Molekülen H2O pro Formeleinheit sind a0=14·67±0·15 Å, b0=13·12±0·07 Å, c0=7·52±0·10 Å, =111°36. Das Diffraktionssymbol ist 1 2/m 1 C ... mit den möglichen Raumgruppen C 2-C 2 3 Cm-C s 3 und C 2/m-C 2h 3 . Falls die in der Literatur aufscheinende Angabe der Kristallklasse von Laumontit mit 2/m-C2h als gesichert angesehen werden kann, ist die Raumgruppe C 2/m-C 2h 3 . Nach dem positiven piezoelektrischen Effekt, bestimmt durch D.S. Coombs (1952) ist die Raumgruppe Cm-C s 3 oder C 2-C 2 3 . In der bestimmten Zelle haben vier Formeleinheiten CaAl2Si4O12. 4 H2O Platz.Mit 1 Textabbildung.  相似文献   

17.
A geothermometer equation \(T = \frac{{1531}} {{\ln K_d + 0.883}}\), where \(K_{\dot d} = \frac{{X_{Zr}^S X_{Hf}^m }} {{X_{Zr}^m X_{Hf}^s }}\) [X j i is the concentration (in ppm) of component i in phase j] is the Zr and Hf distribution coefficient between melt and zircon, and T is temperature in K, was derived by thermodynamic processing of literature experimental data on Zr and Hf distribution between acid melts (m) and zircon (s) and on the solubility of zircon and hafnon in the melts with variable silica content. In calculations with this equations, we assumed the Zr concentration in zircon to be constant: 480000 ppm. It is shown that the commonly observed increase in Hf concentration from the cores to margins of magmatic zircon crystals is caused by the fractional crystallization of zircon. For differentiated acid magmatic series, the initial crystallization temperature of zircon in the least silicic cumulates should be evaluated using the cores of large zircon grains with the highest Zr/Hf ratio. Application of the geothermometer for mafic and intermediate rocks may be hampered due to simultaneous crystallization of zircon with some other ore and mafic minerals relatively enriched in Zr and Hf. The newly derived geothermometer has some advantages over other indicators of the crystallization temperature of magmatic zircon based on the zircon saturation index (Watson and Harrison, 1983; Boehnke et al., 2013) and on Ti concentration in this mineral (Ferry and Watson, 2007) as it does not depend on the major-oxide melt composition and on the accuracy of the estimated SiO2 and TiO2 activities in the melts. Calculations of the Zr and Hf fractionation trends in the course of zircon crystallization in granitoid melts allow one to evaluate the temperature at which more evolved melt portions were segregated.  相似文献   

18.
Zusammenfassung KZnCl3 · 2H2O kristallisiert in der Raumgruppe P 21/a-C 2h 5 mit a =12,03 Å ; b =10,09 Å c =6,26 Å, =107,5° und Z =4. Die Kristallstruktur wurde aus Patterson-Schnitten bestimmt. Die Zink werden von drei Chlor und einem Wassermolekül tetraedrisch umgeben; die Kalium von sieben Chlor und einem Wassermolekül.Die Parameter wurden nach der Methode der kleinsten Quadrate verfeinert.
KZnCl3 · 2H2O crystallizes with unit cell dimensions a=12,03 Å; b=10,09 Å; c=6,26 Å, =107,5°. The space group is P21/a-C 2h 5 with Z=4.The structure has been determined by Patterson methods. Zinc is tetrahedrally surrounded by three chlorine and one H2O, potassium is surrounded by seven chlorine and one H2O. The structure has been refined three-dimensionally by the method of least-squares.

Herrn Prof. Dr.C. W. Correns zum 70. Geburtstag gewidmet.  相似文献   

19.
The space group and hydrogen positions of -(Al0.84Mg0.07Si0.09)OOH are investigated using a single crystal synthesized using a multi-anvil apparatus under conditions of 1000 °C and 21 GPa. The space group determined by single-crystal X-ray diffraction is to Pnn2, with unit-cell parameters of a=4.6975(8) Å, b= 4.2060(6) Å, c=2.8327(4) Å, and V=55.97(1) Å3. Partial occupancy of the Al site by Mg and Si suggests the possibility of a limited solid solution between -AlOOH, stishovite, and a hypothetical CaCl2-type Mg(OH)2 that is 16% denser than brucite. Difference-Fourier maps reveal two small but significant Fourier peaks attributable to hydrogen atoms. Atomic distances and angles around the first peak indicate a hydrogen bond with O···O distances of 2.511 Å, while those around the second peak are suggestive of a bifurcated hydrogen bond with O···O distances of 2.743 and 2.743 Å.  相似文献   

20.
Zusammenfassung Wasserfreies Eisen(III)sulfat, Fe2(SO4)3, existiert in zwei Modifikationen. Nach Einkristallaufnahmen kristallisiert die eine wahrscheinlich in Raumgruppe (arh=8,791±0,004 Å, =55°52±2; Z=2), die andere in Raumgruppe C 2h 5 –P21/n (a=8,296±0,002 Å, b=8,515±0,002 Å, c=11,60±0,002 Å, =90°30; Z=4). Von Cr2(SO4)3 und Ga2(SO4)3 konnten für die rhomboedrischen Modifikationen, die isotyp zu jener von Fe2(SO4)3 sind, aus Pulveraufnahmen die Gitterkonstanten bestimmt werden.
Summary Anhydrous iron(III)sulfate exists in two modifications. From single-crystal work, one of the modifications crystallizes probably in space group (arh=8.791±0.004 Å, =55°52±2; Z=2), whereas the other in space group C 2h 5 –P21/n (a=8.296±0.002 Å, b=8.515±0.002 Å, c=11.60±0,002 Å, =90°30; Z=4). The lattice constants of the rhombohedral modifications of Cr2(SO4)3 and Ga2(SO4)3, which are isomorphous with rhombohedral Fe2(SO4)3, have been determined from powder photographs.

Herrn Professor Dr.F. Machatschki zum 70. Geburtstag gewidmet.  相似文献   

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