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1.
A Ca- and Mn-poor clino-amphibole with Mg/Mg+Fetot+Mn (atomic ratio)=0.81 is described. The structural formula is $$Na_{0.09} (Ca_{0.19} Mg_{5.45} Fe_{1.23}^{2 + } Mn_{0.04} Fe_{0.00}^{3 + } Ti_{0.01} Al_{0.07} )_{6.99} [(Si_{7.83} Al_{0.17} )_{8.00} O_{22} /(OH)_2 ].$$ The unit-cell constants area 0=9.49 Å,b 0=18.00 Å,c 0=5.30 Å, β=102.0°,V 0=886 Å3, the refractive indices αNa=1.621, βNa=1.632, and γNa=1.643. These values, when plotted against the Mg/Mg+Fe ratio, fit the extrapolations towards Mg7[Si8O22/(OH)2] from recently published determinative curves for the cummingtonite series. The clino-amphibole, or part of it, has space groupP21/m rather thanC2/m. The most magnesian cummingtonites reported thus far have Mg/Mg+Fe+Mn ratios around 0.7, but recently more magnesian Ca-poorP21/m clino-amphiboles have been reported. Although Ca and Mn have been claimed to stabilize cummingtonite as against anthophyllite, most magnesian cummingtonites appear to have <0.24 Ca, and <0.1 Mn per formula unit. The nomenclature of the cummingtonite series is discussed. Retaining the subdivision of the cummingtonite series at Mg/Mg+Fe=0.5, the author proposes to reviveTilley’s (1939) name magnesiocummingtonite for members with Mg/Mg+Fe >0.5. Grunerite is reserved for members with Mg/Mg+Fe <0.5. The space group,C2/m orP21/m, may be indicated with a suffix, if known.  相似文献   

2.
Magnesium silicate perovskite is the predominant phase in the Earth’s lower mantle, and it is well known that incorporation of iron has a strong effect on its crystal structure and physical properties. To constrain the crystal chemistry of (Mg, Fe)SiO3 perovskite more accurately, we synthesized single crystals of Mg0.946(17)Fe0.056(12)Si0.997(16)O3 perovskite at 26 GPa and 2,073 K using a multianvil press and investigated its crystal structure, oxidation state and iron-site occupancy using single-crystal X-ray diffraction and energy-domain Synchrotron Mössbauer Source spectroscopy. Single-crystal refinements indicate that all iron (Fe2+ and Fe3+) substitutes on the A-site only, where \( {\text{Fe}}^{ 3+ } /\Upsigma {\text{Fe}}\sim 20\,\% \) based on Mössbauer spectroscopy. Charge balance likely occurs through a small number of cation vacancies on either the A- or the B-site. The octahedral tilt angle (Φ) calculated for our sample from the refined atomic coordinates is 20.3°, which is 2° higher than the value calculated from the unit-cell parameters (a = 4.7877 Å, b = 4.9480 Å, c = 6.915 Å) which assumes undistorted octahedra. A compilation of all available single-crystal data (atomic coordinates) for (Mg, Fe)(Si, Al)O3 perovskite from the literature shows a smooth increase of Φ with composition that is independent of the nature of cation substitution (e.g., \( {\text{Mg}}^{ 2+ } - {\text{Fe}}^{ 2+ } \) or \( {\text{Mg}}^{ 2+ } {\text{Si}}^{ 4+ } - {\text{Fe}}^{ 3+ } {\text{Al}}^{ 3+ } \) substitution mechanism), contrary to previous observations based on unit-cell parameter calculations.  相似文献   

3.
A garnet-clinopyroxene geothermometer based on the available experimental data on compositions of coexisting phases in the system MgO-FeO-MnO-Al2O3-Na2O-SiO2 is as follows: $$T({\text{}}K) = \frac{{8288 + 0.0276 P {\text{(bar)}} + Q1 - Q2}}{{1.987 \ln K_{\text{D}} + 2.4083}}$$ where P is pressure, and Q1, Q2, and K D are given by the following equations $$Q1 = 2,710{\text{(}}X_{{\text{Fe}}} - X_{{\text{Mg}}} {\text{)}} + 3,150{\text{ }}X_{{\text{Ca}}} + 2,600{\text{ }}X_{{\text{Mn}}} $$ (mole fractions in garnet) $$\begin{gathered}Q2 = - 6,594[X_{{\text{Fe}}} {\text{(}}X_{{\text{Fe}}} - 2X_{{\text{Mg}}} {\text{)]}} \hfill \\{\text{ }} - 12762{\text{ [}}X_{{\text{Fe}}} - X_{{\text{Mg}}} (1 - X_{{\text{Fe}}} {\text{)]}} \hfill \\{\text{ }} - 11,281[X_{{\text{Ca}}} (1 - X_{{\text{Al}}} ) - 2X_{{\text{Mg}}} 2X_{{\text{Ca}}} ] \hfill \\{\text{ + 6137[}}X_{{\text{Ca}}} (2X_{{\text{Mg}}} + X_{{\text{Al}}} )] \hfill \\{\text{ + 35,791[}}X_{{\text{Al}}} (1 - 2X_{{\text{Mg}}} )] \hfill \\{\text{ + 25,409[(}}X_{{\text{Ca}}} )^2 ] - 55,137[X_{{\text{Ca}}} (X_{{\text{Mg}}} - X_{{\text{Fe}}} )] \hfill \\{\text{ }} - 11,338[X_{{\text{Al}}} (X_{{\text{Fe}}} - X_{{\text{Mg}}} )] \hfill \\\end{gathered} $$ [mole fractions in clinopyroxene Mg = MgSiO3, Fe = FeSiO3, Ca = CaSiO3, Al = (Al2O3-Na2O)] K D = (Fe/Mg) in garnet/(Fe/Mg) in clinopyroxene. Mn and Cr in clinopyroxene, when present in small concentrations are added to Fe and Al respectively. Fe is total Fe2++Fe3+.  相似文献   

4.
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   

5.
Minerals of the triphylite-lithiophilite, Li(Fe, Mn)PO4, and the triplite-zwieselite-magniotriplite series, (Mn, Fe, Mg)2PO4F, occur in the late stage period of pegmatite evolution. Unfortunately, neither are the genetic relationships between these phosphates fully understood nor are thermodynamic data known. Consequently, phosphate associations and assemblages from 8 granitic pegmatites — Clementine II, Rubicon II and III, and Tsaobismund (Namibia); Hagendorf-Süd and Rabenstein (Germany); Valmy (France); Viitaniemi (Finland) — have been tested for compositional zoning and intercrystalline partitioning of main elements by electron microprobe techniques. Although the selected pegmatites display varying degrees of fractionation, and the intergrowth textures indicate different genetic relationships between the phosphates, the plots of mole fractions X Fe=Fe/(Fe+Mn+Mg+Ca), X Mn=Mn/(Fe+Mn+Mg+Ca), and X Mg=Mg/(Fe+Mn+Mg+Ca) can be fitted relatively well with smooth curves in Roozeboom diagrams. Their deviations from symmetrical distribution curves are mainly dependent upon X Mg or X Ca, and upon non-ideal solutions. Surprisingly small differences between the partition coefficients were detected for intergrowths of different origin. However, the partitioning of shared components among coexisting phases is clearly dependent upon the conditions of formation. Compositional zoning is observed only when both Fe–Mn phosphates are intergrown mutually or with other Fe–Mn–Mg mineral solid-solutios. Thus, the zoning does not seem to be due to continuous crystallization, but to later diffusion processes. The triplite structure has preference for Mn, Mg, and Ca, while Fe prefers minerals of the triphylite series. A quantification of main element fractionation between minerals of the triphylite and the triplite series is possible in the cases where diffusion can be excluded. For the Fe/(Fe+Mn) ratios of core compositions an equation with a high correlation coefficient (R=0.988) was determined: Fe/(Fe+Mn)Tr=[Fe/(Fe+Mn)Li]/{2.737-(1.737)[Fe/(Fe+Mn)Li]} (Tr=triplite series, Li=triphylite series). Consequently, the Fe/(Fe+Mn) ratio of the triplite series can now also be used in the interpretation of pegmatite evolution, just like that of the triphylite series which has been successfully applied in the past.  相似文献   

6.
Heyrovskýite has a composition range from 6(Pb0.83Bi0.10(Ag, Cu)0.07) S . Bi2S3 to 6(Pb0.92Bi0.05(Ag, Cu)0.03) S . Bi2S3. It is orthorhombic. Crystal forms {100}, {010}, {120}, {140}, {250}, and {321} (?) were observed; {010} and {140} are dominant. Elongated c, flattened (010). a:b:c morph=0.432:1:0.128. Cell parameters a=13.705±0.013 Å, b=31.194±0.033, c=4.121±0.003, a:b:c X-ray=0.439:1:0.132. The diffraction symbol is Bb, compatible with Bbmm, Bb21 m, Bbm2. Morphology corresponds to point groups mmm or mm2, reducing the possible space groups to Bbmm and Bbm2. Density at 20 °C is 7.17 g/cm3, calculated, 7.18; Z=4. Micro-indentation hardness (VHN) (50 g load) is 166 to 234 kp/mm2. Strongly anisotropic; reflectance strongly variable, roughly the same as of galena. Etch tests: HNO3 (1:1) and HCl (1:1) positive, FeCl3 20%, HgCl2 5%, KCN 20%, and KOH 40% all negative. Powder data are identical with those for phase II of Otto and Strunz (1968). Heyrovskýite is associated with galena and cosalite at H?rky, Czechoslovakia.  相似文献   

7.
The Taiping-Huangshan batholith in southeast China is a polygenetic composite granitoid consisting of two parts. The northern part is known as the Taiping granodiorite, genetically designated to the Syntexis-type granitoids of southeast China[1] or I-type[4]. Based on whole-rock Rb-Sr isochron dating, its age is 22 3 m. y. with a relatively low initial Sr ratio (0.7069), suggesting that it was emplaced during the Indosinian period. The southern part, the Huangshan multi-staged granite, is genetically ascribed to the transformation type of southeast China, or S-type, which includes two bodies known as the Huangshan and Shizilin granites. Both were formed in the late Yenshanian period as indicated by their ages: 131 m.y. for the Huangshan granite and 123 m. y. for the Shizilin granite, and high initial Sr ratios (0.714 for the Huangshan granite and 0.718 for the Shizilin granite) determine using whole-rock Rb-Sr isochron dating method. The biotite in the Taiping granodiorite is Mg-biotite with a high Mg/(Mg +ΣFe + Mn +VIAl3+) ratio (> 0.42) in its octahedral layers, and has a longerc-axis (10.220–10.224 Å) and a larger unit-cell volume (499.5 Å3), as calculated from X-ray powder diffraction data But the biotites in the Huangshan and Shizilin granies occur mostly as siderophyllite, subsequently as Fe-biotite and occasionally as zoned mica consisting of siderophyllite and musco-vite. The Mg/(Mg +ΣFe + Mn +VIAl3+) ratios are low, whileVIAl3+/(Mg+ΣFe+Mn+VIAl3+) ratios high in their octahedral layers. They have a shorterc-axis (10.128–10.196A) and a small nit-cell volume (494.5 Å3 on average). Comparison of their chemical compositions and corresponding unit-cell parameters for 13 samples from the batholith indicates that thec-axis length increases with increasing Mg content with a noticea ble positive correlation between them, but decreases with increasingVAl3+ content, showing an obvious negative correlation. The changes of theb-axis lengths with the compositions of biotites are much less pronounced than that of thec-axis length.  相似文献   

8.
Fifteen samples of (Mg,Fe)SiO3 majorite with varying Fe/Mg composition and one sample of (Mg,Fe)(Si,Al)O3 majorite were synthesized at high pressure and temperature under different conditions of oxygen fugacity using a multianvil press, and examined ex situ using X-ray diffraction and Mössbauer and optical absorption spectroscopy. The relative concentration of Fe3+ increases both with total iron content and increasing oxygen fugacity, but not with Al concentration. Optical absorption spectra indicate the presence of Fe2+–Fe3+ charge transfer, where band intensity increases with increasing Fe3+ concentration. Mössbauer data were used in conjunction with electron microprobe analyses to determine the site distribution of all cations. Both Al and Fe3+ substitute on the octahedral site, and charge balance occurs through the removal of Si. The degree of Mg/Si ordering on the octahedral sites in (Mg,Fe)SiO3 majorite, which affects both the c/a ratio and the unit cell volume, is influenced by the thermal history of the sample. The Fe3+ concentration of (Mg,Fe)(Si,Al)O3 majorite in the mantle will reflect prevailing redox conditions, which are believed to be relatively reducing in the transition zone. Exchange of material across the transition boundary to (Mg,Fe) (Si,Al)O3 perovskite would then require a mechanism to oxidize sufficient iron to satisfy crystal-chemical requirements of the lower-mantle perovskite phase.  相似文献   

9.
Cordierite samples from pegmatites and metamorphic rocks have been analysed for major [electron microprobe analysis (EMPA)] and trace elements [inductively coupled plasma mass spectrometry (ICP-MS), secondary ion mass spectrometry analyses (SIMS)] as well as for H2O and CO2 (coulometric titration), and the results evaluated in conjunction with published data in order to determine which exchange mechanisms are significant. Apart from the homovalent substitutions FeMg−1 and MnMg−1 on the octahedral site, some minor KNa−1 on the Ch0 channel site, and Fe3+Al−1 on the T11 tetrahedral site, the three most important substitution mechanisms are those for the incorporation of Li on the octahedral sites (NaLi□−1Mg−1), and of Be and other divalent cations on the tetrahedral T11 site (NaBe□−1Al−1 and Na(Mg,Fe2+)□−1Al−1). The dominant role of the last vector is clearly demonstrated. We propose a new generalized formula for cordierite: Ch(Na,K)0–1 VI(Mg,Fe2+,Mn,Li)2 IVSi5 IVAl3 IV(Al, Be, Mg, Fe2+, Fe3+)O18 *xCh(H2O, CO2…). Our results show that the population of (Mg, Fe2+) on the T11-site is limited to about 0.08 a.p.f.u. Other exchange mechanisms that were encountered in experiments operate only under P–T conditions or in bulk compositions that are rarely realized in nature. Routine analyses by electron microprobe in which Li and Be are not determined can be plotted as (Mg+Fe+Mn) versus (Si+Al) to assess whether significant amounts of Li and Be could be present. These amounts can be calculated as Li (a.p.f.u.)=Al+Na–4 and Be (a.p.f.u.)=10–2Al–M2+–Na.  相似文献   

10.
With the aim of better understanding geochemistry of coal, 71 Late Permian whole-seam coal channel samples from western Guizhou Province, Southwest China were studied and 57 elements in them were determined. The contents of Al, Ca, Co, Cr, Cu, Fe, Ga, Hf, K, Li, Mn, Mo, Nb, Ni, Sn, Ta, Ti, Th, U, V, Zr, and REEs in the Late Permian coals from western Guizhou Province are higher than the arithmetic means for the corresponding elements in the US coals, whereas As, Ba, Br, F, Hg, P, Se, and Tl are lower. Compared to common Chinese coals, the contents of Co, Cr, Cu, Ga, Hf, Li, Mn, Mo, Ni, Sc, Sn, Ti, U, V, Zn, and Zr in western Guizhou coals are higher, and As, F, Hg, Rb, Sb, Tl, and W are lower. Five groups of elements may be classified according to their mode of occurrence in coal: The first two, Group A, Tm–Yb–Lu–Y–Er–Ho–Dy–Tb–Ce–La–Nd–Pr–Gd–Sm, and Group B, As–Sr–K–Rb–Ba–F–Ash–Si–Sn–Ga–Hf–Al–Ta–Zr–Be–Th–Na, have high positive correlation coefficients with ash yield and they show mainly inorganic affinity. Some elements from Group B, such as Ba, Be, Ga, Hf, and Th, are also characterized by significant aluminosilicate affinity. In addition, arsenic also exhibits high sulfide affinity (rS–Fe>0.5). The elements, which have negative or lower positive correlation coefficients with ash yield (with exceptions of Bi, Cs, Nb, Mn, Se, and Ti), are grouped in other four associations: Group C, Cr–V–Mo–U–Cd–Tl; Group D, Hg–Li–Sc–Ti–Eu–Nb–Cs–W; Group E, Bi–Sb; and Group F, Co–Ni–Cu–Pb–Zn–Mg–Se–Ca–Mn–S–Fe. The correlation coefficients of some elements, including Co, Cr, Cu, Fe, Hg, Li, Mo, Ni, P, S, Sc, U, V, and Zn, with ash yield are below the statistically significant value. Only Cr and Cu are negatively correlated to ash yield (−0.07 and −0.01, respectively), showing intermediate (organic and inorganic) affinity. Manganese and Fe are characterized by carbonate affinity probably due to high content of epigenetic veined ankerite in some coals. Phosphorus has low correlation coefficients with any other elements and is not included in these six associations. There are five possible genetic types of enrichment of elements in coal from western Guizhou Province: source rock, volcanic ash, low-temperature hydrothermal fluid, groundwater, and magmatic hydrothermal inputs.  相似文献   

11.
The non-ideal regular Mg-Fe binary in cordierite has been derived through multivariate linear regression of the expressionRT InKD +(P- 1)ΔVK 1 0 , 298 along with updated subfegular mixing parameter of almandine-pyrope solution (Hackler and Wood 1989; Berman 1990). The data base used for multivariate analyses consists of published experimental data (n = 177) on Mg-Fe partitioning between garnet and cordierite in theP-T range 650–1050°C and 4–12 K bar. The non-ideality can be approximated by temperature-dependent Margules parameters. The retrieved values of ΔH<T> o and ΔH<T> o of exchange reaction between garnet and cordierite and enthalpy and entropy of mixing of Mg-Fe cordierite were combined with recent quaternary (Fe-Mg-Ca-Mn) mixing data in garnet to obtain the geothermometric expressions to determine temperature (T Kelvin): $$\begin{gathered} T(WH) = 6832 + 0.031(P - 1) - \{ 166(X_{Mg}^{Gt} )^2 - 506(X_{Fe}^{Gt} )^2 + 680X_{Fe}^{Gt} X_{Mg}^{Gt} + 336(X_{Ca} + X_{Mn} ) \hfill \\ (X_{Mg} - X_{Fe} )^{Gt} - 3300X_{Ca}^{Gt} - 358X_{Mn}^{Gt} \} + 954(X_{Fe} - X_{Mg} )^{Crd} /1.987\ln K_D + 3.41 + 1.5X_{Ca}^{Gt} \hfill \\ + 1.23(X_{Fe} - X_{Mg} )^{Crd} \hfill \\ \end{gathered} $$ $$\begin{gathered} T(Br) = 6920 + 0.031(p - 1) - \{ 18(X_{Mg}^{Gt} )^2 - 296(X_{Fe}^{Gt} )^2 + 556X_{Fe}^{Gt} X_{Mg}^{Gt} - 6339X_{Ca}^{Gt} X_{Mg}^{Gt} \hfill \\ - 99(X_{Ca}^{Gt} )^2 + 4687X_{Ca}^{Gt} (X_{Mg} - X_{Fe}^{Gt} ) - 4269X_{Ca}^{Gt} X_{Fe}^{Gt} - 358X_{Mn}^{Gt} \} + 640(X_{Fe} - X_{Mg} )^{Crd} \hfill \\ + 1.90X_{Ca}^{Gt} (X_{Mg} - X_{Ca} )^{Gt} . \hfill \\ \end{gathered} $$   相似文献   

12.
Cu- and Mn-bearing tourmalines from Brazil and Mozambique were characterised chemically (EMPA and LA-ICP-MS) and by X-ray single-crystal structure refinement. All these samples are rich in Al, Li and F (fluor-elbaite) and contain significant amounts of CuO (up to ~1.8 wt%) and MnO (up to ~3.5 wt%). Structurally investigated samples show a pronounced positive correlation between the <Y-O> distances and the (Li + Mn2+ + Cu + Fe2+) content (apfu) at this site with R 2 = 0.90. An excellent negative correlation exists between the <Y-O> distances and the Al2O3 content (R 2 = 0.94). The samples at each locality generally show a strong negative correlation between the X-site vacancies and the (MnO + FeO) content. The Mn content in these tourmalines depends on the availability of Mn, on the formation temperature, as well as on stereochemical constraints. Because of a very weak correlation between MnO and CuO we believe that the Cu content in tourmaline is essentially dependent on the availability of Cu and on stereochemical constraints.  相似文献   

13.
NaBe-cordierites (Fe/(Fe+Mn+Mg)=0.49–0.57) with BeO contents up to 1.16 weight % and additional Li2O contents up to 0.21 wt.% occur in cordierite-apatite-uraninite-muscovite-biotite-chlorite-feldspar-quartz nodules within pegmatites penetrating gneissic roof pendants of a lower Palaeozoic granite batholith. Occasional small crystals of beryl are interpreted to coexist stably with unaltered cordierite. Be and Li are incorporated in cordieriteaccording to the substitutions Na[Channel] + Be[4] Al[4] and Na[Ch]+Li[6]R2+[6], respectively. The coexisting phyllosilicates do apparently not contain appreciable amounts of Li. According to powder IR-data, the analyzed water contents of the cordierites are dominantly of type II, and there is also little CO2. Their distortion indices are rather low (0.121–0.145) and so are their optic angles (2V=50-51°). Considering all eleven NaBeLi-cordierites known thus far there is a strong positive correlation between Na and (Be+Li) with a slope close to 1.0. However, there is virtually no correlation between Be and Li, their incorporation into cordierite depending on the local geochemical environment. A strong negative correlation exists between the distortion indices of the NaBeLi-cordierites and their Be contents. Li has a disturbing influence on this relationship, and the versus Na correlation is also statistically worse than versus Be.Deceased December 20, 1984  相似文献   

14.
Biotites from unaltered Sn granites in southeastern Australia are highly ferroan, Fe/(Fe+Mg+Mn) >0.75, whereas biotites from barren granites are less Ferich, Fe/(Fe+Mg+Mn)<0.65. Similar distinctions between Sn-specialized and barren granites can be observed in the other phyllosilicates, especially chlorite. Biotites and muscovites from Sn granites have greater Be, Cs, (F), Li, Mo, Rb, Sc, Sn, Tl, (Y) and Zn and lesser Ba abundances than corresponding micas from barren granites in the same district. Alteration of barren granites also results in similar enrichments in micas. Of these elements, Sn and Zn, because of their abundance and retention during degradation of biotite to chlorite, are the best trace element discriminants between barren granites and Sn granites/altered granites, with the Sn content of phyllosilicates being a better indicator than Zn. Rutile inclusions within phyllosilicates from unaltered Sn granites have Nb2O5 contents up to 26%. The Ta content tends to increase with Nb content but especially high Ta contents occur in the rutile inclusions of granites that give rise to pegmatitic deposits. The rutile inclusions in Sn granites may also have substantial Sn and W contents. The rutiles of barren granites have low Nb, Ta, Sn and W contents but Sn and W increase with alteration. Together, the ratio Fe/(Fe+Mg+Mn) and Sn contents in phyllosilicates and rutile compositions can be used to identify the Sn mineralization potential of a granite.  相似文献   

15.
(Mg,Fe)(Si,Al)O3 perovskite samples with varying Fe and Al concentration were synthesised at high pressure and temperature at varying conditions of oxygen fugacity using a multianvil press, and were characterised using ex?situ X-ray diffraction, electron microprobe, Mössbauer spectroscopy and analytical transmission electron microscopy. The Fe3+/ΣFe ratio was determined from Mössbauer spectra recorded at 293 and 80?K, and shows a nearly linear dependence of Fe3+/ΣFe with Al composition of (Mg,Fe)(Si,Al)O3 perovskite. The Fe3+/ΣFe values were obtained for selected samples of (Mg,Fe)(Si,Al)O3 perovskite using electron energy-loss near-edge structure (ELNES) spectroscopy, and are in excellent agreement with Mössbauer data, demonstrating that Fe3+/ΣFe can be determined with a spatial resolution on the order of nm. Oxygen concentrations were determined by combining bulk chemical data with Fe3+/ΣFe data determined by Mössbauer spectroscopy, and show a significant concentration of oxygen vacancies in (Mg,Fe)(Si,Al)O3 perovskite.  相似文献   

16.
A natural 1 M-celadonite from Barcza, Poland, approximates closely the Mg-Al end member of the celadonite group. The lattice constants of this phase are $$a_0 = 5.208 \pm 0.005{\AA},b_0 = 9.006 \pm 0.003{\AA}, c_0 = 10.071 \pm 0.004{\AA}, \beta = 1$$ . A comparison with other end members indicates that within this group of minerals the substitution Mg+Si=2 Al diminishes c 0, whereas the incorporation of Fe+3 instead of octahedral Al will increase both b 0 and c 0 sin β.  相似文献   

17.
Mordenite is a zeolite whose approximate composition is (Na2, K2,Ca)4[Al8Si40O96] 28 H2O. Unit cell dimensions, determined by X-ray powder diffractometry for 35 natural samples, fell within the following ranges: a=18.052–18.168, b=20.404–20.527, c=7.501–7.537 Å. The indexed powder pattern of a typical sample is reported. Complete wet chemical analyses of 12 samples, partial analyses of three others, and 6 analyses from the literature reveal that mordenites vary only slightly in chemical composition. Si occupies 80 to 85% of the tetrahedra, and the exchangeable cations are mainly Na and Ca, with minor K. The lattice constant b is negatively correlated to the ratio Si/(Si+Al+Fe?).  相似文献   

18.
Single-crystal X-ray and neutron structure refinements carried out on neptunite (KNa2Li(Fe, Mg, Mn)2Ti2Si8O24) from San Benito, California at various temperatures (neutrons: 15 K and 293 K; X-rays: 110 K, 293 K and 493 K) indicate that this mineral crystallizes in the acentric space group Cc (T=293K: a=16.427 Å, b=12.478 Å, c=9.975 Å, = 115.56°, Z=4, V=1844.53 Å3) due to ordering of octahedrally coordinated metals (Ti, Fe, Mn, Mg). In the neptunite structure, Ti and (Fe, Mn, Mg) octahedra share edges to form chains that run along [110] and [110]. These chains are, in turn, linked through shared corners along [001]. The resulting octahedral framework is interwoven by a similar [Si8O22] tetrahedral framework. Li, Na and K occupy 6-, 8- and 10- coordinated sites within the framework. The metal-containing polyhedra show strong distortions at all temperatures. In particular, Ti exhibits a strong off-center displacement (0.25 Å) within its octahedron, leading to four Ti-O distances of 2.0 Å, one of 2.2 Å and one of 1.7 Å. The displaced Ti position is in good agreement with a position that minimizes differences between ionic bond strengths and is interpreted as an energy minimum in an ionic potential model. Mössbauer spectra collected at 77 K, 293 K and 400 K indicate all Fe to be present as octahedral Fe2+. Although two distinct Fe positions were found in the structure, 77 K and 293 K spectra display only one quadrupole doublet. Two Fe sites can only be resolved in the 400 K spectrum. It is suggested that the temperature dependence of octahedral edge distortions is responsible for the separation of the Mössbauer doublets.  相似文献   

19.
任静  李超  刘宇平  武振坤  任磊 《岩矿测试》2018,37(3):275-282
经历反复埋藏暴露演化过程的河流阶地样品,难以用常规方法将原生宇宙核素10Be、26Al有效分离。本文在前人实验方法基础上,使用人工挑选、磁选仪分选及酸洗方法,分离样品中碳酸盐、含铁矿物及大气生成的10Be,进一步优化了石英提纯实验流程。结果表明:长度为9 cm、内径为1 cm的阴离子交换树脂装置匹配4 mol/L氢氟酸淋滤液,可将B、Mg、Ca、Cr、Fe、Mn、Ni、Ti和Be、Al有效分离,Be、Al回收率分别可达95.7%、85.7%。阳离子交换树脂能有效分离Be、Al,两元素回收率均达到85%。获得10Be/9Be和26Al/27Al流程空白分别为2.19×10-15和1.63×10-15。优化后的实验方法显著提高了河流阶地样品中原生宇宙核素10Be、26Al的纯化效率,且10Be/9Be和26Al/27Al流程空白数值与国内外实验室具有可比性。采用本方法获得了成都平原冲积物10Be、26Al暴露年龄分别是76.36±9.51 ka和69.44±14.13 ka,为评价龙门山前缘隐伏断裂构造特征和活动性提供了年代学依据。  相似文献   

20.
The water quality of the Vacacaí River was assessed at different sites in the period between winter 2005 and autumn 2006. All samples were analyzed for 52 elements (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, Li, Be, Mg, Al, Ca, V, Cr, Mn, Fe, Ni, Co, Cu, Zn, Ga, As, Se, Rb, Sr, Ag, Cd, In, Cs, Ba, Tl, Pb, Bi, U, Na, K, Hg, B, Mo, Sn, Te, Ti), temperature, pH, ammonia, and alkalinity levels. Water from the Vacacaí River ranged from slightly acidic to alkaline. No difference was observed in the chemical composition at different sites of the Vacacaí River. Levels of Ba, Ca, Sr and Mg increase in the dry seasons and reach their highest concentrations in autumn; Be and U decrease in the dry season and reach their highest concentration in spring. Al, Fe, Cr, Ni, Th, U Mn, Ca and Mg are highly positively related, indicating a common origin. Se and Cu are probably from anthropogenic source, from the rice crops of the margins of the river. Waterborne Al and Fe levels were above the desirable level for drinking water at all sites during all seasons. These results demonstrate the need for constant monitoring of water parameters, which is crucial to ensure water quality for the population of this region.  相似文献   

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