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1.
Natural samples of K-feldspar representing various states of Al, Si order were characterised using X-ray methods, transmission electron microscopy, and Fourier transform infrared spectroscopy. Line profiles of infrared absorption bands were observed to show strong correlation with the degree of Al, Si order present. In particular, the absorption frequencies of the 540 cm?1 and 640 cm?1 bands were seen to vary by ca. 10 cm?1 between sanidine and microcline, with modulated samples respresenting intermediate behaviour. Linewidths of these modes also decrease by ca. 50% in this series. The experimental results are discussed within the framework of Hard Mode Infrared Spectroscopy (HMIS), and it is shown that the absorption frequencies vary with the short range order parameter τ = (4t1-1)2 and the symmetry breaking order parameter describing Al, Si order, Q od=(t1 0?t1 m)/Q od=(t1 0+t1 m), where t1 is the average Al occupancy on the T1 sites and t1 o and t1 m are the individual site occupancies of the T1 o and T1 m sites, respectively. The structural state of orthoclase is characterised by strain-induced modulations with large spatial variations of the modulation wavelength. No such modulations were observed in the degree of local Al, Si order. Sanidine shows mode hardening in excess of the extrapolated effect of symmetry breaking Al, Si order, which is presumably related to nonsymmetry breaking ordering between T1 and T2 sites and/or as yet unobserved short range order of the symmetry breaking ordering scheme. The possibility of an additional phase transition in K-feldspar at temperatures above 1300 K is discussed.  相似文献   

2.
Hard Mode Infrared Spectroscopy (HMIS) is used to correlate the line shifts Δω, the intensity changes ΔA and the variations of spectral line widths Γ of infrared absorption bands with the degree of Al, Si ordering, Q od, in kinetically disordered Na-feldspar. A simple relationship Δω∝ΔA∝ΔΓ∝Q od 2 was found with the phonon band around 650 cm?1 being particularly sensitive to small changes of the degree of Al, Si ordering. It is shown that the average degree of Al, Si order can be determined from HMIS with an accuracy of ca. 8 percent using 50 mg of Na-feldspar. The experimental results agree well with recent X-ray determinations using identical samples. The significance of HMIS for the study of kinetic processes in minerals is explained.  相似文献   

3.
Polarized IR spectra of planeparallel (0001) plates of synthetic smoky quartz, with E rotating around [0001], show that the absorption figures of OH– related absorption bands at 3380 (room temperature), 3365 and 3305 cm–1 (liquid nitrogen temperature, -196° C) are strongly anisotropic and violate the trigonal symmetry of low quartz. This effect is correlated with a non-uniform substitution of Si by Al on the three symmetrically equivalent Si sites, as revealed by EPR measurements. Random distribution of Al over the three Si sites, obtained by dry annealing of the samples in air, yields isotropic absorption figures in the (0001) plates. It is thus experimentally evident that the absorption bands at 3380, 3365 and 3305cm–1 are caused by the OH– stretching vibrations coupled with Al substituting for Si. For each experimentally determined integral absorption coefficient of the three absorption bands a theoretical absorption coefficient was calculated, based on the symmetry of low quartz and the given Al distribution. This was done for various orientations of the OH– dipoles with respect to the a axes of low quartz. By comparing the experimentally determined and calculated absorption coefficients, the orientation of the corresponding OH– dipoles with respect to the a axes could be determined.  相似文献   

4.
Thermal transformations of kaolinite of different degree of crystallinity have been monitored by 27Al and 29Si high-resolution NMR with magic-angle spinning (MAS NMR), X-ray diffraction, Fourier transform infrared, atomic absorption spectrophotometry and thermogravimetric analysis. NMR shows differences in the dehydroxylation process of kaolinites with different degree of crystallinity and reveals the presence of short-range order in metakaolinite. 29Si NMR spectra acquired with a 30 s recycle delay of poorly and highly crystalline samples heated at 480 and 500° C, respectively, contain three distinct signals; we discuss their assignment in the light of experiments involving leaching of the samples with aqueous KOH. Ca. 40% of Si sites retain their original Q 3 symmetry just above the onset of dehydroxylation and the Q 4 environment is present showing that a small amount of amorphous silica has already segregated. The spectrum of samples treated at 1000° C contains a signal at -110ppm (from Q 4 silicons) and a faint resonance, from mullite, at ca. -87 ppm. 29Si NMR also shows that cristobalite germs are already present at 950–1000° C. The 27Al MAS NMR spectra of metakaolinite reveal the presence of 4-, 5-and 6-coordinated Al. Changes in the three Al populations as a function of temperature have been monitored quantitatively. Below 800° C, 4-and 5-coordinated Al appears at the expense of 6-coordinated Al, but above 800° C the amount of 6-coordinated Al increases again. We suggest a dehydroxylation scheme which accounts for the presence of 4-and 5 coordinated Al. Above 900–950° C the latter signal is no longer present in the 27Al NMR spectra and new 4-and 6-coordinated Al species (mullite and γ-alumina) appear. We propose new ideas for the structure of metakaolinite.  相似文献   

5.
The chemical composition and the crystal structure of pezzottaite [ideal composition Cs(Be2Li)Al2Si6O18; space group: ${\it{R}} \overline{\text{3}} $ c, a?=?15.9615(6) ?, c?=?27.8568(9) ?] from the type locality in Ambatovita (central Madagascar) were investigated by electron microprobe analysis in wavelength dispersive mode, thermo-gravimetric analysis, Fourier-transform infrared spectroscopy, single-crystal X-ray (at 298?K) and neutron (at 2.3?K) diffraction. The average chemical formula of the sample of pezzottaite resulted Cs1,Cs2(Cs0.565Rb0.027K0.017)Σ0.600 Na1,Na2(Na0.101Ca0.024)Σ0.125Be2.078Li0.922 Al1,Al2(Mg0.002Mn0.002Fe0.003Al1.978)Σ1.985 Si1,Si2,Si3(Al0.056Si5.944)Σ6O18·0.27H2O. The (unpolarized) IR spectrum over the region 3,800–600?cm?1 was collected and a comparison with the absorption bands found in beryl carried out. In particular, two-weak absorption bands ascribable to the fundamental H2O stretching vibrations (i.e. 3,591 and 3,545?cm?1) were observed, despite the mineral being nominally anhydrous. The X-ray and neutron structure refinements showed: (a) a non-significant presence of aluminium, beryllium or lithium at the Si1, Si2 and Si3 sites, (b) the absence (at a significant level) of lithium at the octahedral Al1, Al2 and Al3 sites and (c) a partial lithium/beryllium disordering between tetrahedral Be and Li sites.  相似文献   

6.
Hard mode Raman spectroscopy (HMRS) on hypersolvus alkali feldspar shows a temperature dependence of the order parameter of the displacive \({{C2} \mathord{\left/ {\vphantom {{C2} {m{\text{ - }}C\bar 1}}} \right. \kern-0em} {m{\text{ - }}C\bar 1}}\) phase transition following mean-field behaviour: $$Q \sim \sqrt {T_c - T;} 300 {\text{K}} \lesssim T< T_c $$ At lower temperatures, a spontaneous saturation sets in, which is attributed to site-ordering effects of the alkali atoms even in hypersolvus anorthoclase. Fluctuational line broadening of Si-O viration bands is explained by strong lattice distortions around alkali positions and local deformation of the Al,Si,O network. The thermodynamic relevance of these distortions is discussed in relation to the possibility of an additional diffuse phase transition occurring atT d =302 K. The experimental results of HMRS are compared with those on Al,Si ordered and disordered albite, where no fluctuation broadening occurs.  相似文献   

7.
The infrared (IR) spectra of gem-quality olivine crystals from Pakistan, formed in serpentinised dunitic rocks, are characterised by strongly pleochroic absorption bands at 3,613, 3,597, 3,580 and 3,566 cm?1. These bands are assigned to O-H stretching vibrations of OH point defects corresponding to H2O concentrations of about 35 wt ppm. Unlike other olivine spectra, the dominating bands are strongly polarised parallel to the b-axis. The unusual spectra type, excludes the presence of planar defects. This finding is supported by transmission electron microscopy. The 3,613 cm?1 band is related to vacant Si sites, the slightly lower energetic bands preferentially to vacant M2 sites. The exclusive presence of these bands is not only a characteristic feature of olivines treated under high P,T conditions equivalent to mantle environment, the presence of these bands in untreated natural olivine also indicates formation conditions equivalent to crustal rocks.  相似文献   

8.
《Chemical Geology》2006,225(3-4):360-372
Powder IR absorption spectroscopy has been used to characterise cation substitutions in three garnet solid solutions: grossular–andradite, skiagite–andradite and skiagite–almandine. The wavenumber shift of the highest energy mode associated with tetrahedral vibrations depends on the type of cation occupying the adjacent sites in the structure. The wavenumber shifts exhibit positive deviations from linearity that correlate closely with the variations of the Si–O bond distances for all three garnet solid solutions. The autocorrelation function has been used to determine an effective line width (Δcorr) of the absorption bands over a given spectral region. Non-linear behaviour of Δcorr was found for all three solid solutions. An empirical calibration between Δcorr excess and calorimetric enthalpy of mixing data gives an estimate for the symmetric Margules parameters WspecH of the three solid solutions. Comparison with the systematics of aluminosilicate garnets in terms of WspecH vs. ΔV2, where ΔV represents the difference in molar volume between the end members in a binary system, reveals that such a relationship is not generally applicable to garnet solid solutions with an octahedral cation other than Al.  相似文献   

9.
Observation of major bands seen in infrared spectra of 26 phyllosilicates (23 of which were produced in the laboratory) are reported for wave numbers from 50 to 280 cm?1. Substitutions in the various structural sites (interlayer, tetrahedral and octahedral) permit one to identify the ions which contribute to the vibrations which give rise to bands in the infrared spectra. No attempt is made to assign vibrational modes or specific vibrational types. Using the following ion substitutions, OH-OD; Na-K-Sr-Mg-Ca; Si-Ge; Al-Ga; Mg-Co-Ni-Fe, it is apparent that in the 7 Å chlorite (amesite and chrysotile), kaolinite, pyrophyllite, aluminous dioctahedral mica, aluminous smectites and trioctahedral micas it is not possible to attribute any low frequency bands as being dominated by interlayer ion stretch vibrations (alkali ions). The cations which participate in the vibrators responsible for the dominant modes observed then seem to be Si and Al. This does not exclude the existence of interlayer ion stretch modes in these spectral regions, however they could not be identified. In the materials studied only a few bands can be attributed to hydroxyl-related vibrations and little influence is seen for octahedrally coordinated ions in dioctahedral minerals. It is important to note that the lowest frequency bands (80–140 cm?1) are apparently dominated by vibrations in the network and especially to the Si-O part of the structure. Low frequency bands are however most apparent in charged layer structures, i.e. micas and smectites.  相似文献   

10.
武素茹  宋义  谷松海  郭芬  孙鑫 《岩矿测试》2015,34(6):659-664
鉴别锰矿与锰冶炼渣对于锰矿进口贸易和环境保护具有重要意义,由于锰冶炼渣与一些锰矿具有相似的元素组成,都含有锰和硅铝镁钙等杂质元素,仅从元素含量的高低无法准确将其鉴别。本文按国别收集我国主要进口锰矿及不同工艺的主要锰冶炼渣作为研究样品,应用X射线荧光光谱、X射线衍射及傅里叶变换红外光谱技术相结合,建立了锰矿与锰冶炼渣的鉴别方法。在元素组成上,锰冶炼渣的硅含量较高,水淬渣和空气冷却渣的钙含量较高。在物相上,锰矿的特征物相包括软锰矿、氧化锰、方锰矿、菱锰矿等;而锰冶炼渣因为经过冶炼的过程存在硅酸铁、锰橄榄石等特征峰,从而对样品属性进行鉴别。红外光谱显示,锰矿在600~400 cm~(-1)范围内有两个强吸收带,并单独或者同时在1420 cm~(-1)处有特征吸收峰;而锰冶炼渣在960 cm~(-1)左右有宽强吸收峰。本法建立了锰矿的物相谱图库及锰冶炼渣的物相特征,并充分利用红外光谱技术作了有力佐证,确定了锰矿及其冶炼渣的主要区别点。  相似文献   

11.
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   

12.
Normal coordinate calculations, producing synthetic infrared and Raman spectra, were carried out on melilites, pyroxenes, silica polymorphs and feldspars. Atomic motions are complex in the high-frequency Raman modes of melilites and aluminous pyroxenes. The symmetric T-Onb stretching vibrations of Si and Al tetrahedra with different numbers of bridging oxygens are separate from each other, but may combine individually with oscillation of bridging oxygens between Si and Al tetrahedra. The latter type of vibration tends to dominate as Al/Si increases. The frequencies of these vibrational components and the degree of such intermixing depend on T-O force constants, which vary greatly depending on local bonding configurations; individual bands in the high-frequency Raman cannot in general be assigned to single structural entities or fixed combinations thereof. Calculations confirm that in some Al-Si glasses such as jadeite and spodumene, i.e. those in which all Al can be tetrahedral without non-bridging oxygens, Al-O-Al linkages or linkage of more than two tetrahedra by a single oxygen, aluminum is predominantly in tetrahedral coordination. Other Al-Si glasses which are richer in aluminum or which have non-bridging oxygens may contain Al tetrahedral triclusters, non-tetrahedral Al, or both. On the basis of distinctive 450–750 cm?1 infrared bands, both silica and feldspar glasses resemble tridymite and related stuffed derivatives, not other crystalline silica polymorphs or feldspars. Either these glasses have a structure like that of tridymite on a local scale, or the disorder of the glasses causes drastic modification to the vibrations in question.  相似文献   

13.
The natural occurrence of hydroxide in olivine   总被引：1，自引：0，他引：1  
Polarized infrared (IR) spectra of olivine single crystals from 17 different localities show a tremendous variability in both mode and abundance of hydroxide (OH) incorporation. Kimberlitic olivines contain the most total OH at an estimated concentration level of 976 H/106Si, whereas olivines from basalts contain the least at 3 H/106Si. Olivines of metamorphic and hydrothermal origin have widely varying concentration levels intermediate between those of basalts and kimberlites. Over 30 distinct OH absorption bands have been identified. Most of these bands are not unique to individual localities but may be found in samples from several different localities. Pleochroism is consistent among localities, but relative band intensities vary. No evidence is found for molecular H2 in olivine. Hydrous minerals have been identified in olivine by their characteristic OH absorption bands. Serpentine is commonly found and is clearly distinguishable from intrinsic OH. Talc is present in one sample. Prominent OH bands at 3572 and 3525 cm?1 are attributed to humite group minerals. San Carlos, Arizona, olivines annealed in the presence of H2O develop absorption bands which are found in natural samples, however the OH absorption spectra of these annealed olivines are not identical to those of any single natural crystal. Sharp-band OH abundances in annealed samples are an order of magnitude lower than the maximum measured in natural specimens. The mechanical properties determined from these annealed olivines may not be directly applicable to mantle olivine because both the OH sites and concentrations are different.  相似文献   

14.
The lattice parameters of anorthites An98Ab2 and An100 have been measured from 22 to 1100 K. The spontaneous strain arising from the \(I\overline 1 - P\overline 1\) displacive transition in An98 follows second order Landau behaviour. The spontaneous strain (? s) couples quadratically to the order parameter (Q 0) with ? s∝Q 02∝(T c * ?T) and T c * =530 K in An98. This is in contrast to the tricritical behaviour observed in pure anorthite. These observations are consistent with a Landau model for the free energy of Ca-rich plagioclases in which Al/Si order and Na content renormalize the fourth order coefficient.  相似文献   

15.
Effect of some additives on synthesis of zeolite from coal fly ash   总被引：3，自引：0，他引：3  
Hydrothermal conversion of fly ash into zeolites was conducted and the effects of the addition of sodium halide and waste solutions produced after zeolitization of fly ash, as well as the adjustment of the Si/Al ratio prior to synthesis process on the formation and cation exchange capacity (CEC) of zeolite product were evaluated. Both the addition of NaCl and NaF ameliorated the crystallinity and CEC of synthesized zeolite, but NaF had a better improvement effect. Na+ was considered to enhance the crystallization of zeolite, while F− favored the dissolution of fly ash. The type of zeolite formed depended on the Si/Al ratio of the starting material prior to the nucleation and crystallization of zeolite. The adjustment of the Si/Al ratio of fly ash by addition of Na2SiO4 and Al(OH)3 changed the type and CEC of zeolite. Waste solutions contained large amount of Si and little Al due to the formation of a zeolite named NaP1 in zeolite terminology with the Joint Committee of Powder Diffraction Standard (JCPDS) code of 39-0219. The alkalinity decreased largely. As a result, the CEC value of zeolite products synthesized with waste solution as alkali source decreased. The supplementation of new alkali to adjust the alkalinity of waste solution could enhance the CEC of synthesized product. It was concluded that: (1) addition of sodium halide and adjustment of the Si/Al ratio prior to synthesis can improve the quality of zeolite; (2) waste solutions produced following the zeolitization of fly ash can be reused as an alkali source in the activation of fly ash; zero-emission of waste solution in the synthesis of zeolite from fly ash is possible.  相似文献   

16.
A method of determining the number of Al-O-Al bonds per unit cell from 29Si nuclear magnetic resonance (NMR) data of synthetic cordierites with increasing Si, Al order is described. The number of Al-O-Al bonds is found to vary linearly with the logarithm of the annealing time. This may be correlated with previously published heat of solution data on similar samples (Carpenter et al. 1983) to determine the enthalpy change Δh, associated with a single Al?Si interchange in cordierite. Δh is found to be 8.1 kcal/mole. The NMR data show that the short range Al, Si order cannot be described in terms of twin domains of ordered orthorhombic cordierite. An ordering model derived from group theoretical constraints on possible Al, Si distributions within the hexagonal symmetry of the cordierite is found to provide a better fit to the NMR data.  相似文献   

17.
《Applied Geochemistry》2005,20(7):1357-1367
Cancrinite, sodalite, and zeolite A have been found to form upon contacting hyperalkaline simulated tank waste (STW) with vadose zone sediments from the Hanford Reservation. Here, soluble silica and STW are used to study mineral formation and transformation. Two Hanford sediment fractions (diameters <50 and >50 μm instead of soluble silica) are also used as silica sources for comparison. A series of batch experiments at 50 °C and 25 days duration were conducted by reacting 0.026 mol/kg soluble Si with 6 different STW solutions. The STW solutions differed in NaOH and Al concentrations. Cancrinite, sodalite, and zeolite A formed when soluble Si was used as the Si source. The minerals were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and 27Al and 29Si magic-angle spinning nuclear magnetic resonance (MAS-NMR). Larger NaOH and Al concentrations favored formation of the more compact structures of cancrinite and sodalite. At larger NaOH concentration more Al for Si substitution occurred in the tetrahedral sites. A greater Al(4)/Al(6) ratio in the solids was found for the higher Si/Al ratio solutions based on NMR results. Mixtures of cancrinite and sodalite were characterized by particles with lepispheric morphology. At low Al concentration, increasing NaOH resulted in distinct hexagonal, prismatic particles common to crystalline cancrinite. At low Al/Si ratio, the characteristic cubic morphology of zeolite was observed in addition to cancrinite and sodalite.  相似文献   

18.
Feldspars crystallized in the range SrF80An20-SrF60An40 of the join CaAl2Si2O8-SrAl-2Si2O8 from gels at T = 1350–1500° C for short time show cell parameters significantly different from those obtained from longer heating. This difference has been interpreted as due to higher metastable Al/Si disorder in short heated samples and to more ordered configurations with longer heat treatments. HT powder spectra show that the T c of the Iī-I2/c phase transition of feldspars changes with composition and with the degree of order at constant composition; the evolution of the spontaneous strain (～cosα*) versus T for the samples examined shows a variation in the order of the transition from continuous (II order) in more ordered and Sr-rich samples to a discontinuous behaviour (presumably I order) for more disordered and Sr-poor samples. A biquadratic coupling between displacive and OD parameters is therefore suggested.  相似文献   

19.
A detailed evaluation of the assignments given to the infrared (IR) vibrations in the lattice stretching region is presented here based on observations of the effects of various chemical substitutions in synthetic analogues of phlogopite, KMg3(AlSi3)O10(OH)2. As in previous studies, this study has confirmed that the 995, 960, and 460 cm?1 vibrations are influenced by Si, the 822 and 760 cm?1 vibrations by Al, the 915 and 725 cm?1 vibrations by Al and Si, and the 592 cm?1 vibration by OH. Contrary to previous studies, it is shown here that the 690, 495, and 375 cm?1 vibrations are strongly linked with Mg and not just Si. The 655 cm?1 band in phlogopite is attributed to an in-plane Al-O vibration rather than an Al-O-Si vibration. As a check on the band assignments made here, IR spectra were obtained for synthetic clintonite, CaMg2Al(Al3Si)O10(OH)2, as well as its chemical analogues and compared with the IR spectrum of phlogopite. The band intensities for the Si-O, Al-O, and Si-O-Mg vibrations changed in accord with the composition of clintonite. The most intense band in clintonite at 660 cm?1 appears to be associated only with Al and is assigned here to a tetrahedral Al-O-Al vibration which must be present, if not dominant, in this mineral. The near coincidence of an in-plane Al-O vibration at 655 cm?1 (phlogopite) and an in-plane Al-O-Al vibration at 660 cm?1 (clintonite) makes the identification of tetrahedral Al-Si order-disorder in trioctahedral layered silicates by IR spectroscopy very difficult. The ratio of the 822/995 cm?1 bands may, however, prove to be very useful for discerning the amount of tetrahedrally coordinated Al in these types of minerals.  相似文献   

20.
Landau theory of the \(P\bar 1 - I\bar 1\) phase transition in Ca-rich plagioclases reveals the sensitivity of the phase transition behaviour to a) Al, Si disorder, b) structural replacement of Ca by Na, and c) inhomogeneities of lattice strains. The following effects are predicted:
  1. A tricritical phase transition exists in fully ordered anorthite. Al, Si disorder and Na, Ca exchange lead to second order phase transitions.
  2. The transition temperatures depend sensitively on the degree of Al, Si disorder and the chemical composition of the Ca-rich plagioclases. Increasing Na-content decreases the transition temperatures.
  3. The thermal evolution of c and d reflections depends on the homogeneity of the crystal and do not necessarily reflect the temperature evolution of the macroscopic lattice strain. A simple quadratic dependence of the X-ray scattering intensity on the order parameter exists only for fully ordered, homogeneous anorthite.
The role of inhomogeneous Al, Si distributions and lattice relaxations are discussed including possible structural modulations.  相似文献   

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