An experimental investigation into the metastable formation of phosphoran olivine and pyroxene     

Joseph S. Boesenberg  Roger H. Hewins 《Geochimica et cosmochimica acta》2010,74(6):1923-1941

The formation of phosphoran olivine by crystallization from a melt was investigated experimentally using a one atmosphere furnace, using San Carlos olivine [(Mg,Fe)₂SiO₄] mixed with either iron phosphide (FeP) or magnesium pyrophosphate (Mg₂P₂O₇). Both dynamic crystallization and isothermal experiments produced phosphoran olivine as zoned single crystals and as overgrowths surrounding normal, phosphorus-free olivine grains. The crystallization pathways that form phosphoran olivine were traced and confirm that it is a metastable phase that can crystallize from a phosphorus-rich melt over timescales of hours to days. Removal of the P and equilibration of the olivine however requires weeks to months in the presence of silicate melt. Phosphoran olivine with up to 27 wt% P₂O₅ was generated and up to 69% of the Si tetrahedral sites were replaced by P. The substitution of Si by P into olivine was confirmed as 4^VIM⁺² + 2^IVSi⁺⁴ ↔ 3^VIM⁺² + 2^IVP⁺⁵ + ^VI[]. Phosphoran olivine compositions that vary from (Mg,Fe)₂SiO₄ to (Mg,Fe)_1.65[]_0.35Si_0.3P_0.7O₄ have been produced in these experiments.Phosphoran pyroxene was also generated in a few experiments and forms when phosphoran olivine reacts with either tridymite or melt. It has compositions compatible with protopyroxene, orthopyroxene, pigeonite and sub-calcic augite, and can contain up to 31.5 wt% P₂O₅. Like phosphoran olivine, it is also a metastable phase. Phosphorus replaces Si in pyroxene by the following substitution methods: 8^IVSi⁺⁴ ↔ 3^IVSi⁺⁴ + 4^IVP⁺⁵ + ^IV[] with Al entering the structure by the exchange 2^IVSi⁺⁴ ↔ ^IVAl⁺³ + ^IVP⁺⁵. Phosphoran pyroxene compositions vary from (Mg,Fe)₈Si₈O₂₄ to (Mg,Fe)₈Si₃P₄[]O₂₄.  相似文献   

Base metals and other minor elements in the manganese deposits of west-central Arkansas     

G.H. Wagner  Ronald H. Konig  Sidney Vogelpohl  Michael D. Jones 《Chemical Geology》1979,27(4):309-327

Manganese oxides from deposits in west-central Arkansas were analyzed by X-ray diffraction for mineralogy and by atomic absorption spectroscopy for Mn, Fe, Co, Cu, Ni, Zn, V, Al, Li, Na, K, Mg, Ca, Sr and Ba. We report on 42 samples from 25 sites with more than 25 wt.% Mn and less than 7 wt.% Fe. Most samples were mixtures of two or more of the following minerals, many with concentric deposition: cryptomelane, lithiophorite, psilomelane and pyrolusite. In the purer samples of single minerals, lithiophorite contained the higher concentrations of total base metals (Co + Cu + Ni + Zn) than other minerals. In atom % of Mn these concentrations were: 9.51% in lithiophorite; 0.432% in psilomelane; and 0.275% in cryptomelane. The relative concentration of base metals in the pure minerals, proceeding from highest to lowest concentration, were: lithiophorite (Co = Cu > Ni > Zn); psilomelane (Co > Cu > Zn > Ni) and cryptomelane (Zn > Co = Cu > Ni).The concentration of Li correlates with the metals Al, Co, Cu, Ni and Zn, in the mineral samples containing measurable Li. Correlation coefficients (?) for Li with the various metals and sum of the base metals were: Al (? = 0.976); Co (? = 0.44); Ni (? = 0.954); Cu (? = 0.918); Zn (? = 0.875); and (Co + Cu + Ni + Zn) (? = 0.979). Li is believed to be a measure of lithiophorite. Correlation was found between Al content and base metal contents for all samples: Co (? = 0.354); Ni (? = 0.749); Cu (? = 0.808); Zn (? = 0.632); and (Co + Cu + Ni + Zn) (? = 0.884). The Al correlation extended to published values for these and the minerals hollandite and todorokite, except for Zn. Zn correlated with K in published analyses and in the eastern half of the study area where cryptomelane predominated.A mechanism is proposed to explain the enhancement by Al of base metal incorporation into manganese oxide minerals. The mechanism involves the isomorphous substitution of Al³⁺ for Mn⁴⁺ with charge neutralization by bivalent base metal ions.  相似文献   

The preparation and characterization of vanadium-substituted goethite: The importance of temperature     

Navdeep Kaur  Brendan J. Kennedy 《Geochimica et cosmochimica acta》2009,73(3):582-9557

Despite a close geo-chemical association between vanadium (V) and iron (Fe) in natural environments, there is little research on the substitution of V in goethite. To assess the effect of temperature on V-substitution in goethite, a series of V-substituted goethite were prepared under varying synthesis temperatures, and analysed using wet chemical and multi-spectroscopic techniques. Vanadium substitution was inversely related to synthesis temperatures and was hindered by the oxidation of V³⁺ to V^4+/5+ as indicated by X-ray absorption near-edge spectroscopy. The presence of V (V⁵⁺ > V⁴⁺ > V³⁺) at high temperature hindered the nucleation of goethite and crystal growth along particular faces resulting in large-sized and twinned crystals as shown by transmission electron microscopy. The large-sized goethite crystals released more Fe (mmoles) per unit surface area during proton-promoted dissolution than the smaller-sized crystals, which could be due to distorted V^4+/5+ local coordination environments in the mineral structure. The dissolution studies showed a heterogeneous distribution of V and/or crystal defects in goethite crystals. The results show that low synthesis temperatures preserved the oxidation state of V³⁺, which has ionic radius and hydrolytic properties similar to Fe³⁺, and hence resulted in as much as 13.3 mol per cent substitution. The structural stability of the goethite decreased upon V-substitution in order; V³⁺ > V⁴⁺ > V⁵⁺. This research provides important information about the interaction between temperature, V incorporation, and crystal structure properties of goethite for V sequestration and other potentially toxic metal cations.  相似文献   

Revisiting the compositions and volatile contents of olivine-hosted melt inclusions from the Mount Shasta region: implications for the formation of high-Mg andesites     

D. M. Ruscitto  P. J. Wallace  A. J. R. Kent 《Contributions to Mineralogy and Petrology》2011,162(1):109-132

Primitive chemical characteristics of high-Mg andesites (HMA) suggest equilibration with mantle wedge peridotite, and they may form through either shallow, wet partial melting of the mantle or re-equilibration of slab melts migrating through the wedge. We have re-examined a well-studied example of HMA from near Mt. Shasta, CA, because petrographic evidence for magma mixing has stimulated a recent debate over whether HMA magmas have a mantle origin. We examined naturally quenched, glassy, olivine-hosted (Fo_87–94) melt inclusions from this locality and analyzed the samples by FTIR, LA-ICPMS, and electron probe. Compositions (uncorrected for post-entrapment modification) are highly variable and can be divided into high-CaO (>10 wt%) melts only found in Fo > 91 olivines and low-CaO (<10 wt%) melts in Fo 87–94 olivine hosts. There is evidence for extensive post-entrapment modification in many inclusions. High-CaO inclusions experienced 1.4–3.5 wt% FeO^T loss through diffusive re-equilibration with the host olivine and 13–28 wt% post-entrapment olivine crystallization. Low-CaO inclusions experienced 1–16 wt% olivine crystallization with <2 wt% FeO^T loss experienced by inclusions in Fo > 90 olivines. Restored low-CaO melt inclusions are HMAs (57–61 wt% SiO₂; 4.9–10.9 wt% MgO), whereas high-CaO inclusions are primitive basaltic andesites (PBA) (51–56 wt% SiO₂; 9.8–15.1 wt% MgO). HMA and PBA inclusions have distinct trace element characteristics. Importantly, both types of inclusions are volatile-rich, with maximum values in HMA and PBA melt inclusions of 3.5 and 5.6 wt% H₂O, 830 and 2,900 ppm S, 1,590 and 2,580 ppm Cl, and 500 and 820 ppm CO₂, respectively. PBA melts are comparable to experimental hydrous melts in equilibrium with harzburgite. Two-component mixing between PBA and dacitic magma (59:41) is able to produce a primitive HMA composition, but the predicted mixture shows some small but significant major and trace element discrepancies from published whole-rock analyses from the Shasta locality. An alternative model that involves incorporation of xenocrysts (high-Mg olivine from PBA and pyroxenes from dacite) into a primary (mantle-derived) HMA magma can explain the phenocryst and melt inclusion compositions but is difficult to evaluate quantitatively because of the complex crystal populations. Our results suggest that a spectrum of mantle-derived melts, including both PBA and HMA, may be produced beneath the Shasta region. Compositional similarities between Shasta parental melts and boninites imply similar magma generation processes related to the presence of refractory harzburgite in the shallow mantle.  相似文献   

Trace element incorporation into quartz: A combined study by ICP-MS, electron spin resonance, cathodoluminescence, capillary ion analysis, and gas chromatography     

Jens Götze  Michael Plötze  Dieter Klaus Hallbauer 《Geochimica et cosmochimica acta》2004,68(18):3741-3759

Pegmatite quartz from different occurrences in Norway and Namibia was investigated by a combination of ICP-MS, Electron Spin Resonance (ESR), Capillary Ion Analysis (CIA) and Gas Chromatography (GC) to quantify trace elements in very low concentrations and to determine their position in the quartz structure.The studied quartz samples show similar geochemical characteristics with low contents of most trace elements. Remarkable are the elevated concentrations of Al (36-636 ppm), Ti (1.6-25.2 ppm), Ge (1.0-7.1 ppm), Na (5.2 to >50 ppm), K (1.6 to >100 ppm) and Li (2.1-165.6 ppm). These elements are preferentially incorporated into the quartz lattice on substitutional (Al, Ti, Ge) and interstitial (Li, Na, K) positions. Li⁺ was found to be the main charge compensating ion for Al, Ge and Ti, whereas some ppm of Na and K may also be hosted by fluid inclusions. Ti may be incorporated as substitutional ion for Si or bound on mineral microinclusions (rutile). The results of the ESR measurements show that there may be a redistribution of alkali ions during irradiation. The diamagnetic [AlO₄/M⁺]⁰ center transforms into the paramagnetic [AlO₄]⁰ center, whilst the compensating ions diffuse away and may be captured by the diamagnetic precursor centers of [GeO₄]⁰ and [TiO₄]⁰ to form paramagnetic centers ([TiO₄/Li⁺]⁰, [GeO₄/Li⁺]⁰).In general, fluid inclusions in pegmatite quartz can be classified as H₂O-CO₂-NaCl type inclusions with water as the predominant volatile. Among the main elements hosted by fluid inclusions in quartz are Na, K, NH₄, Ca, Mg and the anionic complexes Cl⁻, NO₃⁻, HCO₃⁻ and SO₄²⁻. Gas analysis of trapped fluids shows volatile components in the following order of abundance: H₂O > CO₂ > N₂(+) ≥ CH₄ > COS > C₂ and C₃ hydrocarbons. Additionally, traces of Co, Ni, Zn, Pb, and Cu were detected by CIA in fluid inclusions of some samples. There are indications that the REE and Rb are also bound in fluid inclusions, however, the concentrations of these elements are too low to be measured by CIA. Assuming that the REE preferentially occur in fluid inclusions, the typical chondrite normalized REE distribution patterns with tetrad effects and a distinct negative Eu anomaly would reflect the composition of the mineralizing fluid.For a number of elements, especially those with extremely low concentrations, the “type” of incorporation in quartz could not directly be determined. We conclude that these ions either are too large to substitute for the small Si⁴⁺ ion or they are not soluble in the mineralizing fluids to be hosted by fluid inclusions. Some of these elements, which are concentrated in the specific mineralization of certain pegmatites, are not present in elevated concentrations in the paragenetic pegmatite quartz itself. This was observed, for instance, for Be, Cs and Rb in the Li (Be-Cs-Rb) pegmatites of Rubicon or for Nb and Ta for Nb-Ta bearing pegmatites from Norway. It may be concluded that the concentrations of these trace elements in quartz do not reflect the mineralization and that these elements thus, cannot be used as petrogenetic indicator.  相似文献   

S-rich apatite-hosted glass inclusions in xenoliths from La Palma: constraints on the volatile partitioning in evolved alkaline magmas   总被引：3，自引：2，他引：1  

Fleurice Parat  François Holtz  Andreas Klügel 《Contributions to Mineralogy and Petrology》2011,162(3):463-478

The composition of S-rich apatite, of volatile-rich glass inclusions in apatite, and of interstitial glasses in alkaline xenoliths from the 1949 basanite eruption in La Palma has been investigated to constrain the partitioning of volatiles between apatite and alkali-rich melts. The xenoliths are interpreted as cumulates from alkaline La Palma magmas. Apatite contains up to 0.89 wt% SO₃ (3560 ppm S), 0.31 wt% Cl, and 0.66 wt% Ce₂O₃. Sulfur is incorporated in apatite via several independent exchange reactions involving (P⁵⁺, Ca²⁺) vs. (S⁶⁺, Si⁴⁺, Na⁺, and Ce³⁺). The concentration of halogens in phonolitic to trachytic glasses ranges from 0.15 to 0.44 wt% for Cl and from <0.07 to 0.65 wt% for F. The sulfur concentration in the glasses ranges from 0.06 to 0.23 wt% SO₃ (sulfate-saturated systems). The chlorine partition coefficients (D_Cl^{apatite/glass}) range from 0.4 to 1.3 (average D_Cl^{apatite/glass} = 0.8), in good agreement with the results of experimental data in mafic and rhyolitic system with low Cl concentrations. With increasing F in glass inclusions D_F^{apatite/glass} decreases from 35 to 3. However, most of our data display a high partition coefficient (~30) close to D_F^{apatite/glass} determined experimentally in felsic rock. D_S^{apatite/glass} decreases from 9.1 to 2.9 with increasing SO₃ in glass inclusions. The combination of natural and experimental data reveals that the S partition coefficient tends toward a value of 2 for high S content in the glass (>0.2 wt% SO₃). D_S^{apatite/glass} is only slightly dependent on the melt composition and can be expressed as: SO_{3 apatite} (wt%) = 0.157 * ln SO_{3 glass} (wt%) + 0.9834. The phonolitic compositions of glass inclusions in amphibole and haüyne are very similar to evolved melts erupted on La Palma. The lower sulfur content and the higher Cl content in the phonolitic melt compared to basaltic magmas erupted in La Palma suggest that during magma evolution the crystallization of haüyne and pyrrhotite probably buffered the sulfur content of the melt, whereas the evolution of Cl concentration reflects an incompatible behavior. Trachytic compositions similar to those of the (water-rich) glass inclusions analyzed in apatite and clinopyroxene are not found as erupted products. These compositions are interpreted to be formed by the reaction between water-rich phonolitic melt and peridotite wall-rock.  相似文献   

Mineral chemistry and origin of spinel-rich inclusions in the Allende CV3 chondrite     

Alan S. Kornacki  John A. Wood 《Geochimica et cosmochimica acta》1985,49(5):1219-1237

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The Tiger Sulfide Chimney,Yonaguni Knoll IV Hydrothermal Field,Southern Okinawa Trough,Japan: The First Reported Occurrence of Pt–Cu–Fe‐Bearing Bismuthinite and Sn‐Bearing Chalcopyrite in an Active Seafloor Hydrothermal System     

Kaul Gena  Hitoshi Chiba  Katsuo Kase  Kazuo Nakashima  Daizo Ishiyama 《Resource Geology》2013,63(4):360-370

A sulfide chimney ore sampled from the flank of the active Tiger vent area in the Yonaguni Knoll IV hydrothermal field, south Okinawa trough, consists of anhydrite, pyrite, sphalerite, galena, chalcopyrite and bismuthinite. Electron microprobe analysis indicates that the chalcopyrite contains up to 2.4 wt% Sn, whereas bismuthinite contains up to 1.7 wt% Pt, 0.8 wt% Cu and 0.5 wt% Fe. The Sn‐rich chalcopyrite and Pt–Cu–Fe‐bearing bismuthinite are the first reported occurrence of such minerals in an active submarine hydrothermal system. The results confirm that Sn enters the chalcopyrite as a solid solution towards stannite by the coupled substitution of Sn⁴⁺Fe²⁺ for Fe³⁺Fe³⁺, whereas Pt, Cu and Fe enter the bismuthinite structure as a solid solution during rapid nucleation. The fluid inclusions homogenization temperatures in anhydrite (220–310°C) and measured end‐member temperature of the vent fluids on‐site (325°C) indicate that Sn‐bearing chalcopyrite and Pt–Cu–Fe‐bearing bismuthinite express the original composition of the minerals that precipitated as metastable phases at a temperature above 300°C. The result observed in this study implies that sulfides in ancient volcanogenic massive sulfide deposits have similar trace element distribution during nucleation but it is remobilised during diagenesis, metamorphism or supergene enrichment processes.  相似文献   

Shock wave-induced interaction between meteoritic iron and silicates     

D. D. Badjukov  V. S. Rusakov  Yu. G. Kupin 《Petrology》2012,20(4):347-355

The possibility of shock wave-induced interaction between meteoritic iron was estimated based on the results of experiments on the shock wave loading of mixtures of kamacite from the Sikhote Alin iron meteorite with quartz, albite, oligoclase, enstatite, olivine, and serpentine. The experimental samples were then examined with the application of optical microscopy, microprobe analysis, and M?ssbauer spectroscopy. As a result of shock wave load, the metal was proved to become enriched in Si, while the quartz, albite, and oligoclase melted glasses acquired bivalent Fe ions. The products of our experiments with quartz and feldspar mixtures with kamacite were determined to contain paramagnetic metallic iron, and the surroundings of iron atoms in the silicate constituent of the olivine and enstatite mixtures with kamacite become locally more heterogeneous. Our results indicate that shock waves induce redox reactions between Fe and silicates according to the scheme 2Fe⁺² + Si⁺⁴ = 2Fe⁺² + Si⁰, where Fe⁰ and Si⁰ are iron and silicon in metal and Fe⁺² and Si⁺⁴ are iron and silicon in the sillimanite matrix.  相似文献   

Computer simulations of the interactions of the (0 1 2) and (0 0 1) surfaces of jarosite with Al, Cd, Cu and Zn     

Karen A. Hudson-Edwards  Kate Wright 《Geochimica et cosmochimica acta》2011,75(1):52-62

Jarosite is an important mineral on Earth, and possibly on Mars, where it controls the mobility of iron, sulfate and potentially toxic metals. Atomistic simulations have been used to study the incorporation of Al³⁺, and the M²⁺ impurities Cd, Cu and Zn, in the (0 1 2) and (0 0 1) surfaces of jarosite. The calculations show that the incorporation of Al on an Fe site is favorable on all surfaces in which terminal Fe ions are exposed, and especially on the (0 0 1) [Fe₃(OH)₃]⁶⁺ surface. Incorporation of Cd, Cu or Zn on a K site balanced by a K vacancy is predicted to stabilize the surfaces, but calculated endothermic solution energies and the high degree of distortion of the surfaces following incorporation suggest that these substitutions will be limited. The calculations also suggest that incorporation of Cd, Cu and Zn on an Fe site balanced by an OH vacancy, or by coupled substitution on both K and Fe sites, is unfavorable, although this might be compensated for by growth of a new layer of jarosite or goethite, as predicted for bulk jarosite. The results of the simulations show that surface structure will exert an influence on uptake of impurities in the order Cu > Cd > Zn, with the most favorable surfaces for incorporation being (0 1 2) [KFe(OH)₄]⁰ and (0 0 1) [Fe₃(OH)₃]⁶⁺.  相似文献   

Seasonal variation in bacterial heavy metal biosorption in water samples from Eziama river near soap and brewery industries and the environmental health implications     

I. Kanu  O. K. Achi  O. U. Ezeronye  E. C. Anyanwu 《International Journal of Environmental Science and Technology》2006,3(1):95-102

Seasonal variation in bacterial heavy metals biosorption from soap and brewery industrial effluent samples from Eziama River in Abia State were analyzed for Pb, Hg, Fe, Zn, As, and Mn, using atomic absorption spectrophotometry. Bioaccumulation of the metals by bacteria showed the following trend > Fe >Zn >As > Pb > Mn (Rainy Season) and Zn > Fe > Mn > As > Hg > Pb (Dry season). Statistical analysis using of variance (ANOVA) showed significant differences in concentrations of Pb, Hg, Fe, Zn, As, and Mn level between the sampling zones at Eziama River. Seasonal changes in heavy metal concentrations, showed increases in Pb, Fe, and As from 1.32 x 10⁵ mg/L in the rainy season to 1.42 x 10⁵ mg/L in the dry season. Fe increased from 40.35 x 10⁵ mg/L to 42.1 x 10⁵ mg/L, while As increased from 2.32 to 2.48 x 10⁵ mg/L with a net increases of+56 and + 69 x 10⁵ mg/L respectively. However, Hg, Zn, and Mn concentrations decreased in the rainy season from 40.54 x 10⁵ mg/L to 39.24 x 10⁵ mg/L, 1.65 to 0.62 x 10⁵ mg/L respectively.  相似文献   

Study on the Physical and Chemical Conditions of Ore Formation of Hetai Ductile Shear Zone—Hosted Gold Deposit and Discovery of Melt Inclusions   总被引：1，自引：0，他引：1  

李兆麟  翟伟  李文  石贵勇  文拥军 《中国地球化学学报》2002,21(1):40-51

The Hetai ductile shear zone-hosted gold deposit occurs in the deep-seated fault mylonite zone of the Sinian-Silurian metamorphic rock series. In this study there have been discovered melt inclusions, fluid-melt inclusions and organic inclusions in ore-bearing quartz veins of the ore deposit and mylonite for the first time. The homogenization temperatures of the various types of inclusions are 160℃, 180 - 350℃, 530℃ and 870℃ for organic inclusions, liquid inclusions, two-phase immiscible liquid inclusions and melt inclusions, respectively. Ore fluid is categorized as the neutral to basic K+ -Ca2+ -Mg2+ -Na+ - SO2- 4-HCO3-Cl- system. The contents of trace gases follow a descending order of H2O＞CO2＞CH4＞(or ＜ ) H2＞CO＞C2H2＞C2I-I6＞O2＞N2.The concentrations of K , Ca2 + ,SO2-4,HCO3-,Cl- H2O and C2H2 in fluid inclusions are related to the contents of gold and the Au/Ag ratios in ores from different levels of the gold deposit. This is significant for deep ore prospecting in the region. Daughter minerals in melt inclusions were analyzed using SEM. Quartz, orthoclase, wollastonite and other silicate minerals were identified. They were formed in different mineral assemblages.This analysis further proves the existence of melt inclusions in ore veins. Sedimentary metamorphic rocks could form silicate melts during metamorphic anatexis and dynamic metamorphism, which possess melt-solution characteristics. Ore formation is related to the multi-stage forming process of silicate melt and fluid.  相似文献   

Electron paramagnetic resonance study of the site preferences of Gd³⁺ and Eu²⁺ in polycrystalline silicate and aluminate minerals     

Richard V. Morris 《Geochimica et cosmochimica acta》1975,39(5):621-634

Electron paramagnetic resonance (EPR) measurements were made on Gd³⁺ and Eu²⁺ ions in polycrystalline samples to determine the nature of the sites occupied by those ions in mineral structures. Both Gd³⁺ and Eu²⁺ ions were incorporated at Ca²⁺ structural sites in β-Ca₂SiO₄, pseudo-CaSiO₃, CaMgSiO₄, CaMgSi₂O₆, hex-CaAl₂Si₂O₈, CaAl₂O₄, and Ca₃Al₂O₆. For tri-CaAl₂Si₂O₈, Eu²⁺ was incorporated at a Ca²⁺ site and Gd³⁺ was incorporated at a site where the crystalline electric field was disordered. That difference in behavior may contribute to the anomalous behavior of Eu in plagioclase feldspar. Both Gd³⁺ and Eu²⁺ were incorporated as aggregates or clusters of those ions in Mg₂SiO₄ and clino-MgSiO₃.  相似文献   

Redox state of iron in peralkaline rhyolitic glass/melt: X-ray absorption micro-spectroscopy experiments at high temperature     

N. Métrich  J. Susini  F. Farges  D. Massare  S. Lequien 《Chemical Geology》2006,231(4):350-363

Assessing the ferric-ferrous ratio in magmas prior to eruption remains a challenging task. X-ray absorption near-edge structure (μXANES) spectra were collected at the iron K-edge in water-rich peralkaline silicic melt/glass inclusions trapped in quartz. These experiments were carried out between 800 and 20 °C. The chemical environment of iron was also determined in the naturally quenched samples (glass inclusions and matrix glass) and in the peralkaline rhyolitic reference glasses, with variable [Fe³⁺ / ∑Fe] ratios.In the reference glasses, both the intensity of the pre-peaks (Fe²⁺, Fe³⁺) and site geometry of iron change as the oxidation state increases. Fourfold-coordinated Fe³⁺ prevails in highly oxidised peralkaline silicic glasses, using alkalis for charge balance. The position of the pre-edge centroid of the 1s-3d transition correlates with the Fe³⁺ / ΣFe ratios that allowed calibration of the redox state of iron of our natural samples.At high temperatures, Fe²⁺ dominates in the pre-edge structure of melt inclusions. Upon cooling down to 20 °C, the intensity of the Fe³⁺ peak increases, the centroid position of the pre-edge features shifts by nearly 0.5 eV and the main edge moves slightly towards higher energies. The slower the cooling rate, the higher the ferric iron contribution. Iterative μXANES experiments performed on the same samples show that the process is reversible. However, this apparent oxidation of iron upon cooling is an artefact of changes in Fe coordination. It implies that the [Fe³⁺ / ΣFe] ratio of glassy samples, measured at 20 °C, may be overestimated by a factor > 1.7, and that this ratio cannot be reliably retrieved by probing naturally cooled glass inclusions, and most silicate glasses. High temperature μXANES experiments led first to an assessment of the ferric-ferrous ratio in the water-rich peralkaline melt in pre-eruptive magmatic conditions and second to the determination of the corresponding oxygen fugacity at 740 °C.  相似文献   

Sapphirine I     

John B. Higgins  Paul H. Ribbe  Richard K. Herd 《Contributions to Mineralogy and Petrology》1979,68(4):349-356

Microprobe analyses of 26 natural sapphirines from 17 localities indicate that the predominant chemical substitutions in this mineral occur along the solid solution join^VI(Mg,Fe)²⁺+^IVSi⁴⁺=^VI(Al, Fe)³⁺+^IVAl³⁺. Chromium and manganese are minor substituents. Evidence for the substitution SiAl+1/2Mg+1/2 vacancy is absent within the limits of analytical error.A partitioning scheme based on electrostatic charge balance considerations has been devised permitting calculation of Fe²⁺ and Fe³⁺ from total iron content. Results are in good agreement with previous Mössbauer studies which indicate Fe³⁺ is sometimes in octahedral and/or tetrahedral coordination.Distribution coefficients for Fe²⁺-Mg exchange equilibria between sapphirine-spinel and sapphirine-orthopyroxene are similar for most mineral pairs and suggest that most of the assemblages equilibrated at about the same temperature or that the exchange reactions are insensitive to temperature.Compositions of synthetic sapphirines as a function of temperature and pressure are qualitatively predictable from crystal chemical considerations. Changes in sapphirine composition along the MgSi= AlAl solid solution join toward more aluminous compositions stabilize the sapphirine structure at high temperatures and low pressures. The limited extent of MgSi=AlAl solid solution observed in natural sapphirines appears to be related to the requirements of geometrical fit among octahedra and tetrahedra in the almost idealized cubic closest-packed anion framework.  相似文献   

IIb trioctahedral chlorite from the Barberton greenstone belt: crystal structure and rock composition constraints with implications to geothermometry   总被引：3，自引：1，他引：3  

Xiaogang Xie  Gary R. Byerly  Ray E. Ferrell Jr. 《Contributions to Mineralogy and Petrology》1997,126(3):275-291

IIb trioctahedral chlorite in the Barberton greenstone belt (BGB) metavolcanic rocks was formed during pervasive greenschist metamorphism. The chem‐ical composition of the chlorite is highly variable, with the Fe/(Fe+Mg) ratio ranging from 0.12 to 0.8 among 53 samples. The chemical variation of the chlorite results from the chemical diversity of the host rock, especially the MgO content of the rock, but major details of the variation pattern of the chlorite are due to the crystal structure of the chlorite. All major cation abundances in the chlorite are strongly correlated with each other. Sil‐icon increases with Mg and decreases with Fe, while Al^IV and Al^VI decrease with Mg and increase with Fe²⁺. A complex exchange vector explains over 90% of the chlorite compositional variation: Mg₄SiFe²⁺ ₋₃Al^VI ₋₁ Al^IV ₋₁, which has 3 parts Fe-Mg substitution coupled with one part tschermakite substitution. This ratio is required to maintain the charge and site balances and the dimensional fit between the tetrahedral and octahedral sheets. The subtle change in Al substitution in chlorite implies that Al^VI is preferentially ordered in the M(4) site, and about 84% of the Al^VI present is in the M(4) sites when they are nearly filled with Al^VI. Based on 47 analyzed chlorite-bearing rock samples, chlorite (Chl) composition is strongly correlated with the MgO content of the host rock. Calculated correlation coefficients are +0.91 for SiO_2Chl-MgO_Rock, −0.87 for Al₂O_3Chl-MgO_Rock, +0.89 for MgO_Chl-MgO_Rock, and −0.85 for FeO_Chl-MgO_Rock. Only weak correlations have been found between chlorite oxides and other oxides of rock (between same oxides in chlorite and rock: SiO₂−0.67, Al₂O₃ + 0.59, FeO −0.41). However, MgO_Chl is saturated at about 36 wt% in rocks that have MgO above 22 wt%.The MgO_Chl is about 5 wt% when the host rock approaches 0 wt% of MgO. This implies that Mg substituting into the chlorite is approximately limited to 1.5–9.2 Mg atoms per formula unit and 1.0–3.2 Al^IV. Chlorite geothermometers can not be applied to all BGB samples. However, the empirical chlorite geothermometer based on Al^IV of chlorite may be applicable to chlorites formed under metamorphic conditions because it can predict the chemical composition of the chlorite from basaltic and dacitic samples in this study. An estimated temperature of about 320°C for the greenschist metamorphism of the greenstone belt through this geothermometer is consistent with that obtained by other geothermometers. Received: 22 January 1996 / Accepted: 15 August 1996  相似文献   

Electric conductivity of Fe2SiO4–Fe3O4 spinel solid solutions     

T. Yamanaka  H. Shimazu  K. Ota 《Physics and Chemistry of Minerals》2001,28(2):110-118

 The spinel solid solution was found to exist in the whole range between Fe₃O₄ and γ-Fe₂SiO₄ at over 10 GPa. The resistivity of Fe_{3− x} Si _x O₄ (0.0<x<0.288) was measured in the temperature range of 80∼300 K by the AC impedance method. Electron hopping between Fe³⁺ and Fe²⁺ in the octahedral site of iron-rich phases gives a large electric conductivity at room temperature. The activation energy of the electron hopping becomes larger with increasing γ-Fe₂SiO₄ component. A nonlinear change in electric conductivity is not simply caused by the statistical probability of Fe³⁺–Fe²⁺ electron hopping with increasing the total Si content. This is probably because a large number of Si⁴⁺ ions occupies the octahedral site and the adjacent Fe²⁺ keeping the local electric neutrality around Si⁴⁺ makes a cluster, which generates a local deformation by Si substitution. The temperature dependence of the conductivity of solid solutions indicates the Verwey transition temperature, which decreases from 124(±2) K at x=0 (Fe₃O₄) to 102(±5) K at x=0.288, and the electric conductivity gap at the transition temperature decreases with Si⁴⁺ substitution. Received: 15 March 2000 / Accepted: 4 September 2000  相似文献   

Titanian andradite in a metapyroxenite layer from the Malenco ultramafics (Italy): implications for Ti-mobility and low oxygen fugacity     

Othmar Müntener  Jörg Hermann 《Contributions to Mineralogy and Petrology》1994,116(1-2):156-168

Ti-andradite (melanite) has been found in a metapyroxenite layer in the upper part of the Malenco ultramafics(Italy), coexisting with clinochlore, diopside and magnetite. Field observations, as well as major and trace elementbulk-rock composition, strongly suggest a cumulate origin for the layer. Textural relationships indicate thatTi-andradite formed during two different metamorphic stages. Under peak metamorphic conditions (400–450°C, 5±2 kbar)Ti-andradite grew in an assemblage of diopside, clinochlore, magnetite and rare ilmenite and perovskite. Later, retrograde brittle deformationinduced formation of veins containing the paragenesis Ti-andradite, vesuvianite, diopside, chlinochlore, magnetite and accessory perovskite.The Ti-andradite varies considerably in TiO₂ (0.11–9.62 wt%), Fe₂O₃(14.3–30.5 wt%), Al₂O₃ (0.65–3.90 wt%), Cr₂O₃(>0.18–0.98 wt%) and SiO₂ (32.1–36.1 wt%); this is mostly, but not entirely, due to distinct zoning.Ti-andradite contains 0.32 to 0.66 wt% H₂O as determined by infrared spectroscopy and 0.83 to 1.76 wt% FeO. The CaO shows almost no variation (34.1±0.7 wt%) and Ca completely fills the dodecahedral site. Single crystal site refinements indicate that no tetrahedral Ti or Fe replaces Si. Titanium incorporation is attributed to similar degrees of substitution along the exchange vectors Ti³⁺ Fe³⁺, Ti⁴⁺ Al^IV Al _-1 ^VI Si_-1 and (Fe²⁺, Mn²⁺, Mg²⁺)Ti⁴⁺ 2Fe _-1 ³⁺ . The presence of mixed valence states of both Fe and Ti suggests a low oxygen fugacity during crystallization of Ti-andradite. Mass balance calculations indicate an isochemical origin of the first generation of Ti-andradite in the clinopyroxenite layer. Its occurrence is restricted to antigorite-free mineral assemblages containing clinochlore of 0.95X _Al>1.1. The hydrothermal crystallization of Ti-rich andradite in veins demonstrates Ti mobility in aqueous fluids under moderate P-T conditions. The zonation patterns indicate disequilibrium conditions during vein crystallization. As no fluorine-, carbonate- and phosphate-bearing minerals were found, OH^- is most probably the ligand complexing Ti.  相似文献   

Prediction of high-temperature oxygen isotope fractionation factors between mantle minerals     

Yong-Fei Zheng 《Physics and Chemistry of Minerals》1997,24(5):356-364

The increment method is adopted to calculate oxygen isotope fractionation factors for mantle minerals, particularly for the polymorphic phases of MgSiO₃ and Mg₂SiO₄. The results predict the following sequence of ¹⁸O-enrichment: pyroxene (Mg,Fe,Ca)₂Si₂O₆>olivine (Mg,Fe)₂SiO₄>spinel (Mg,Fe)₂SiO₄>ilmenite (Mg,Fe, Ca)SiO₃>perovskite (Mg,Fe,Ca)SiO₃. The calculated fractionations for the calcite-perovskite (CaTiO₃) system are in excellent agreement with experimental calibrations. If there would be complete isotopic equilibration in the mantle, the spinel-structured silicates in the transition zone are predicted to be enriched in ¹⁸O relative to the perovskite-structured silicates in the lower mantle but depleted in ¹⁸O relative to olivines and pyroxenes in the upper mantle. The oxygen isotope layering of the mantle would essentially result from differences in the chemical composition and crystal structure of mineral phases at different mantle depths. Assuming isotopic equilibrium on a whole earth scale, the chemical structure of the Earth's interior can be described by the following sequence of ¹⁸O-enrichment: uppr crust>lower crust>upper mantle>transition zone>lower mantle >core.  相似文献   

Red micas from basal ignimbrites of Mt. Vulture (Italy): interlayer content appraisal by a multi-methodic approach     

Fernando Scordari  Emanuela Schingaro  Gennaro Ventruti  Maria Lacalamita  Luisa Ottolini 《Physics and Chemistry of Minerals》2008,35(3):163-174

The crystal chemistry of red phlogopites from Mt. Vulture (Italy) ignimbrites has been studied by electron microprobe, secondary ion mass spectrometry (SIMS), single crystal structural investigation and Fourier transform infrared (FTIR) spectroscopy. The analysed phlogopite has Fe/(Fe + Mg) ∼ 0.35, TiO₂ (wt%): 2.8–5.0 and H₂O (wt%): 1.24–3.37. Infrared spectra revealed the presence of bands due to the NH₄⁺ and H₂O stretching and bending vibrations. The samples belong to the 1M polytype. The bimodal behaviour of several structural parameters allows red micas to be clustered into two distinct groups: K⁺ ↔ NH₄⁺, H₂O and M³⁺-vacancy substitutions dominate in the first group; M^3+,4+-oxy, in the second group. It has to be pointed out that quantitative analysis of hydrogen (via SIMS) together with the characterization of the local environment of the anionic site (via FTIR) are fundamental in assessing the correct structural formula and the substitution mechanisms in micas. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献