Calculated trends of oh infrared stretching vibrations with composition and structure in aluminosilicate molecules

Ab initio, molecular orbital calculations have been performed on a variety of hypothetical aluminosilicate molecules to investigate relationships among composition, structure, and infrared spectra of OH. Vibrational analyses of the full-optimized molecular geometries at the 3–21G^** level were performed with Gaussian 92 to determine theoretical infrared spectra. Theoretical infrared OH frequencies, ν(OH), shift 10 to 100 cm^?1 with ionic substitutions. The inverse correlation of theoretical infrared OH intensities with OH stretching frequencies in these aluminosilicate molecules is similar to that observed for aluminosilicate glasses (Paterson 1982). O-H bond lengths, H-bond distances, and H?nd angles correlate with frequency. The dominant factor affecting ν(OH) is the H-bond distance, if this distance is less than 2 Å. Beyond H-bond distances of 2 Å, structural and compositional effects exert competitive influences on ν(OH).     

Cation segregation and the O-H stretching vibration of the olivenite-adamite series

The behaviour of the O-H stretching infrared spectra of the synthetic olivenite-adamite series described by Brathwaite (1983) is accounted for in terms of the crystal structure and cation distribution. There are three absorption bands: Two at 3,540 and 3,510 cm^?1 correspond to OH groups bonded to Zn₃ and CuZn₂ respectively. The third band corresponds to OH groups bonded to both combinations Cu₂Zn and Cu₃ and its frequency varies with the proportions of those two combinations. Preferential occupation of the five-fold site by Zn is confirmed from its effect on the infrared spectra, the ratio Zn^V/Zn^VI being roughly 4:1. There is evidence for clustering of Zn into Zn₃ groups around OH. Differences in the degree of segregation and clustering of Zn will affect the infrared spectra of natural olivenites and adamites and this may limit the usefulness of infrared spectroscopy as a determinative method.     

OH incorporation in nearly pure MgAl2O4 natural and synthetic spinels

Four nearly pure MgAl₂O₄ spinels, of both natural and synthetic occurrence, have been studied by means of X-ray single crystal diffraction and FTIR spectroscopy in order to detect their potential OH content. Absorption bands that can be assigned to OH incorporated in the spinel structure were only observed in spectra of a non-stoichiometric synthetic sample. The absorption intensity of two bands occurring at 3350 and 3548 cm⁻¹ indicate an OH content of 90 ppm H₂O. Based on correlations of OH vibrational frequencies and O-H?O distances, the observed absorption bands correspond to O-H?O distances of 2.77 and 2.99 Å, respectively, which is close to the values obtained by the structure refinements for ^VIO-O_unsh (2.825 Å) and ^IVO-O (3.001 Å). This indicates that one probable local position for hydrogen incorporation is the oxygens coordinating a vacant tetrahedral site. The present spectra demonstrate that the detection limit for OH in Fe-free spinels is in the range 10-20 ppm H₂O. However, at appreciable Fe²⁺ levels, the detection of OH bands becomes hampered due to overlap with strong absorption bands caused by electronic d-d transitions in Fe²⁺ in the tetrahedral position.     

新疆和田地区大理岩型和田玉的形成及致色因素探讨

采集阿拉玛斯和田玉山料和喀拉喀什河(墨玉河)的和田玉样品,利用显微镜和背散射图像、电子探针等研究手段,结合以往全岩数据对和田玉的形成和致色因素进行了综合分析。研究发现,除透闪石以外,和田玉中还含有大量的绿帘石、透辉石、绿泥石、锆石、磷灰石、尖晶石、石榴石、重晶石、阳起石、闪锌矿、磁黄铁矿、石墨、方解石和氢氧化铁等多种副矿物; Cr、Ni含量(100×10-6)及Mg/(Mg+Fe2+)-Si投点显示这些样品均属于大理岩型软玉(和田玉)。全岩及其微区成分分析结果显示,从白玉(TFe_2O_3=0. 33%～1. 42%)、青白玉(TFe_2O_3=0. 43%～0. 96%)至青玉(TFe_2O_3=0. 77%～3. 97%),TFe_2O_3含量逐渐增加,而且所有样品的Cr和Ni含量都分别低于60×10-6和20×10-6,说明从白玉、青白玉至青玉,颜色的加深与透闪石中铁元素含量逐渐增加有关。墨玉的颜色主要与透闪石集合体中的石墨和Fe(OH)3等细脉大量出现有关。为深入研究和田玉的致色因素,同时采集了加拿大的碧玉样品进行对比,发现同样主要为透闪石组成的加拿大碧玉,除Fe外,还含有大量的Cr元素(1 400×10-6～5 100×10-6),碧玉的颜色鲜艳与透闪石C位中含有0. 01～0. 03 a. p. f. u.的Cr有关,而和田玉中Cr含量较低,在C位中几乎为0。通过野外观察和岩相学分析认为,含和田玉的镁质矽卡岩的形成经历了接触变质、接触交代变质和硫化物阶段,主要通过交代镁质大理岩、透辉石、绿帘石等矿物形成,而和田玉的主要形成机制是多期次的细粒透闪石交代粗粒透闪石。     

高温高压下NaCl-H2O体系的Raman光谱分析: 一种新的流体包裹体盐度测定方法

利用水热金刚石压腔研究了高温高压下0.0%、5.0%、10.0%和20.0%的NaCl-H2O体系的Raman光谱,研究结果发现:对于盐度一定的NaCl-H2O体系,当压力不变时,水的Raman伸缩谱峰的波数变化量△v(O-H)随温度的升高而不断增加;当压力不同时,△v(O-H)随温度的变化关系(偏移斜率S)不受压力的影响,而只与盐度相关.利用该性质可以用来确定流体包裹体的盐度(W),其计算公式如下:W=123.25S2-128.11S+32.40,误差为0.46%.     

F-OH substitution in natural tremolite,talc, and phlogopite

The distribution of F between tremolite and talc has been determined in metamorphosed siliceous carbonates from the Grenville Province, Ontario. Wavelength dispersive electron microprobe analyses of contiguous, texturally compatible tremolite-talc pairs indicate that the substitution of F for OH is the most significant deviation from end-member stoichiometry in the samples studied. Mixing of F and OH components has been represented by an ideal solution model for F in tremolite and an asymmetric model for F in talc. Both linear and nonlinear regression techniques have been used to derive activity coefficients for the exchange of one equivalent of OH and F components in talc. The following expressions are the result of nonlinear regression of 32 analyses from coexisting mineral pairs: $$\begin{gathered} \ln \gamma _{TC(OH)} = X_{TC(F)}^2 [2.447 - 2.845X_{TC(OH)} ] \hfill \\ \ln \gamma _{TC(F)} = X_{TC(OH)}^2 [1.024 + 2.845X_{TC(F} ] \hfill \\ \end{gathered} $$ Isobaric \(T - X_{CO_2 } \) sections constructed using these equations show an enhanced stability for the assemblages talc+calcite and phlogopite+quartz+calcite with F substituting for OH. Projection of isothermal invariant points into P-T space predicts a shift in the stability of the assemblage talc-calcite from lower grade into the sillimanite field with increasing substitution of F for OH in talc.     

Synthetic and natural tremolite in equilibrium with forsterite,enstatite, diopside and fluid

The following equilibrium among tremolite forsterite, diopside, and orthorhombic enstatite has been investigated using either synthetic tremolite or natural amphibole in the starting materials: Ca₂Mg₅Si₈O₂₂(OH)₂+Mg₂SiO₄ =2 CaMgSi₂O₆+5MgSiO₃+H₂O A significant increase in the stability of the reactants was observed with natural rather than synthetic tremolite. For example, in nearly pure H₂O with the H₂ content of the fluid buffered by nickel-bunsenite at one kilobar (10⁸ pascals), the breakdown of the assemblage with synthetic amphibole occurs at 708±20° C. The breakdown of the assemblage with natural amphibole, Ca_2.16Mg_4.94Fe_0.03Si_7.92 Al_0.01O₂₂(OH)₂F_0.03 occurs at 841±47° C. The shift in the breakdown curve is attributed to variation in the properties of the amphiboles since all other factors were common in the experiments. The reactions have also been investigated with hydrogen fugacity defined by the methane buffer and the NB, OH (XG, COH) buffer. Analysis of the experimental data by linear programming indicates that the enthalpy of reaction is tightly constrained when the calorimetrically determined entropy of 160.92 joules/degree is used. The resulting enthalpy of reaction is 113.96±1.82 kilojoules with the natural amphibole and 104.83±0.12 kilojoules with synthetic tremolite. Deviation of the natural amphibole from the ideal tremolite formula as well as a greater number of defects and dislocations in the synthetic amphibole may have contributed to the change in stability.     

A computer simulation study of (OH) defects in olivine

Recent experiments (Miller et al. 1987; Bell and Rossman 1992; Bai and Kohlstedt 1992) have shown that olivine, the dominant mineral in the Earth's upper mantle, can contain substantial amounts of water in the form of OH. There is uncertainty, however, as to the mechanisms by which water dissolves into the mineral structure and as to the site it occupies in the host lattice. We have therefore used atomistic computer simulation techniques based on the Born model of solids, to investigate the structures and energies of OH defects in olivine. Our calculations suggest that the most favourable route for incorporation of OH into olivine involves reactions with water accompanied by the reduction of ferric iron for which we obtain a solution energy of 0.46 eV. We propose therefore that the OH content will be largely controlled by the concentration of Fe³⁺.     

Mechanism of pyroxene and amphibole weathering—I. Experimental studies of iron-free minerals

The short term (2–40 days) dissolution of enstatite, diopside, and tremolite in aqueous solution at low temperatures (20–60°C) and pH 1–6 has been studied in the laboratory by means of chemical analyses of reacting solutions for Ca²⁺, Mg²⁺, and Si(OH)₄ and by the use of X-ray photoelectron spectroscopy (XPS) for detecting changes in surface chemistry of the minerals. All three minerals were found to release silica at a constant rate (linear kinetics) providing that ultrafine particles, produced by grinding, were removed initially by HF treatment. All three also underwent incongruent dissolution with preferential release of Ca and/or Mg relative to Si from their outermost surfaces. The preferential release of Ca, but not Mg for diopside at pH 6 was found by both XPS and solution chemistry verifying the theoretical prediction of greater mobility of cations located in M₂ structural sites. Loss mainly from M₂ sites also explains the degree of preferential loss of Mg from enstatite at pH 6; similar structural arguments apply to the loss of Ca and Mg from the surface of tremolite. In the case of diopside and tremolite initial incongruency was followed by essentially congruent cation-plus-silica dissolution indicating rapid formation of a constant-thickness, cation-depleted surface layer. Cation depletion at elevated temperature and low pH (~ 1) for enstatite and diopside was much greater than at low temperature and neutral pH, and continued reaction resulted in the formation of a surface precipitate of pure silica as indicated by solubility calculations, XPS analyses, and scanning electron microscopy.From XPS results at pH 6, model calculations indicate a cation-depleted altered surface layer of only a few atoms thickness in all three minerals. Also, lack of shifts in XPS peak energies for Si, Ca, and Mg, along with undersaturation of solutions with respect to all known Mg and Ca silicate minerals, suggest that cation depletion results from the substitution of hydrogen ion for Ca²⁺ and/or Mg²⁺ in a modified silicate structure and not from the precipitation of a new, radically different surface phase. These results, combined with findings of high activation energies for dissolution, a non-linear dependence on a_H⁺ for silica release from enstatite and diopside, and the occurrence of etch pitting, all point to surface chemical reaction and not bulk diffusion (either in solution or through altered surface layers) as the rate controlling mechanism of iron-free pyroxene and amphibole dissolution at earth surface temperatures.     

富有机物流体中一些重要Ge同位素的平衡分馏参数

锗（Ge）同位素在地球化学领域有着潜在的应用意义,但是Ge同位素平衡分馏参数的缺乏,严重制约了其在相关研究中的应用。本研究提供了富有机物流体中物种Ge（OH）4、GeO（OH）3^-以及Ge的一些亲有机质络合物（Ge与邻苯二酚、柠檬酸以及草酸配合形成的络合物）之间的Ge同位素平衡分馏参数。用基于Urey模型（或称Bigeleisen-Mayer公式）理论,结合量子化学计算的方法,在B3LYP／6-311＋G（d,p）理论水平下计算了这些Ge同位素平衡分馏系数,其中,溶液效应用精确的“水滴法”来处理。预测这些基本分馏参数的误差约为±0．2‰。纯水溶液中,△Ge（OH）4-GeO（OH）3^-约为0．6‰,海水中稍小,约为0．3‰;而△Ge（OH）4-Ge-邻苯二酚、△Ge（OH）4-Ge-草酸、△Ge（OH）4-Ge-柠檬酸（c）和△Ge（OH）4-Ge柠檬酸（d）非常大,分别约为4．4‰、3．5‰、3．8‰和3．9‰。这些大的分馏或许可以用来示踪生物作用参与过程。结果表明,轻的Ge同位素将富集在富有机质的环境,如煤系、黑色页岩及一些缺氧的条件下,因此这些环境可能存在一个轻Ge同位素的“汇”。     

The intensity of amphibole OH bands in the infrared absorption spectrum

Polarized IR spectra of single-crystals of amphiboles show that the molar absorptivity of the fundamental vibrational OH band is strongly wavenumber dependent. The intensity increases by a factor of 1.6 from 3674 cm^-1 (tremolite endmember; MgMgMg) to 3618 cm^-1 (grunerite endmember; FeFeFe). Spectra obtained from Ca and Fe-Mg amphiboles consist of sharp, well-resolved bands on a well-defined background. The high intensity of the OH bands in Ca and Fe-Mg amphiboles makes it sometimes necessary to thin the samples to under 2 μm thickness, whereas alkali amphiboles can be measured at 25–50 μm thickness.     

NMR applied to minerals. V. The localization of vacancies in the octahedral sheet of aluminous biotites

The localization of vacancies in the octahedral sheet of aluminous biotites has been investigated by the use of ¹H nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. The polytype to which the samples belonged was determined by x-ray diffraction methods. The joint use of all three techniques was essential in determining unambiguously the exact position of the vacancies and orientation of the associated O-H and Fe-H vectors. It was found that vacancies are located in the M1 (pseudo-centrosymmetric) sites and that contrary to what is usually assumed the OH dipoles are not, in this case, oriented directly towards the vacancy site.     

The OH site in topaz: an IR spectroscopic investigation

The OH site in topaz is investigated by IR spectroscopy depending on the OH concentration and temperature. The two OH bands that can be distinguished are due to the local ordering of F and OH in opposite sites of the crystal structure. The first typical sharp band stems from OH groups with fluorine in the opposite (=acceptor) site. The second band occurs as a shoulder on the low-energy wing and is related to two opposite OH groups. The degree of local OH–OH ordering depends on the OH concentration and, due to statistical F/OH distribution, can be predicted by probability calculations. The substitution of OH for F has a non-linear effect on the increase of the lattice parameters. An autocorrelation analysis of the IR spectra revealed two temperature-induced phase transitions. At −135°C, the local symmetry changes from P1 to Pbn2₁, although this change involves only the H atoms. The transition from Pbn2₁ to Pbnm at 160°C is caused by changes of the local F/OH ordering in the crystal structure.     

Ab initio molecular orbital calculations for boron isotope fractionations on boric acids and borates

Ab initio quantum chemistry calculations have been performed on the isotopic exchange reaction between B(OH)₃ and B(OH)₄⁻. Several calculation methods have been carefully compared and evaluated. The “water-droplet” method is chosen to investigate this isotope exchange reaction using cluster models with up to 34 water molecules surrounding the solute. HF/6-31G* level calculations coupled with a 0.920 scaling factor are used for the frequency calculations. A larger K value (1.027) is obtained from this study compared to the commonly used 1.0194 (Kakihana et al., 1977).The fractionations for several boric acid polymers and boron minerals are also studied. Our results suggest that assuming the BO₄ bonding in B(OH)₄⁻ is identical to that in borosilicates is wrong. Tetrahedral boron in silicates has a significantly smaller reduced isotopic partition function ratio (RPFR) and hence will be much isotopically lighter than in B(OH)₄⁻.The new theoretical curve of pH vs. δ¹¹B composition of B(OH)₄⁻ using our calculated 1.027 can be used to predict pH values for equilibrium cases such as incorporation into inorganic calcite. We also find that the shape of this curve is very sensitive to both K and pK_a value, giving the possibility of also predicting salinity from the different shapes of the curve.     

几个重要Ge同位素平衡分馏参数的理论预测

本研究基于Urey模型(或称Bigeleisen和Mayer公式),结合量子化学计算的方法,在B3LYP/6-311+G(d, p)理论水平下,计算了Ge在类似石英(包括蛋白石)、钠长石、钾长石、橄榄石结构以及水溶液(包括海水)中Ge(OH)4和GeO(OH)3-之间的Ge同位素平衡分馏系数.其中,溶液效应用"水滴法"处理,矿物结构用簇合物方法模拟.结果显示这些基本分馏参数的精度约±0.3‰;类石英(或蛋白石)结构最可能富集重Ge同位素,在25 ℃,几个Ge同位素分馏系数分别约为:Δ石英-Ge(OH)4=0.9‰、ΔGe(OH)4-GeO(OH)3-=0.3‰(海水中)、Δ石英-钠长石=0.6‰、Δ石英-钾长石=0.4‰、Δ橄榄石-Ge(OH)4=-1.2‰.类石英与类橄榄石结构之间存在较大的分馏,Δ石英-橄榄石=2.1‰.这些具有重要地质意义的基本分馏参数可以为探索未知的Ge同位素地球化学应用领域打下基础.此外,本文还用所得的分馏参数定量地解释了Siebert等(2006)和Rouxel等(2006)的一些工作,说明了这些参数的可靠性及其在地学中的重要应用意义.     

Structural and IR relations among brucite-like divalent metal hydroxides

The a and c unit cell parameters of M(OH)₂, brucite-like structures with M=Mg, Ni, Co, Fe, Mn, Cd, and Ca, are considered in relation to M-O distances taken as the sum of the ionic radii, M^VI and O^IV. The a parameters are related to (M-O) by flattening of the octahedral coordination groups, with a flattening angle α=97.4±0.4°. The c parameters are divided into the octahedral layer thickness, h(oct), and the interlayer spacing h(inter). The latter is related to the (O-H) distances, which decrease as (M-O) increases. Infrared v(O-H) stretching frequencies vary with (M-O) in the same manner as h(inter) varies with (M-O). The values of v(O-H) decrease as h(inter) decreases and the atomic weight of the cations increases. The results are consistent with previous data for cation-substituted talcs. It is suggested that the M²⁺ ions associated with the O^2? ions modify the reduced mass of the O-H vibrations so that v(O-H) decreases with increasing mass of M.     

Use of ultrasonically modulated electron resonance to study S-state ions in mineral crystals: Mn2+, Fe3+, in tremolite

The use of ultrasonically modulated electron resonance (UMER) to study S-state ions in substitutional sites of mineral single crystals is discussed. Mn²⁺ and Fe³⁺ in natural single crystals of tremolite are used as examples. Combined electron paramagnetic resonance (EPR) and UMER measurements establish almost certainly that Mn²⁺ enters predominantly into the distorted M4 sites occupied by Ca²⁺ in the ideal tremolite structure and only to a minor extent into the M1, M2 and M3 sites normally occupied by Mg²⁺. Fe³⁺ in tremolite gives rise to the well known high spin resonance with g _eff?4.3 but there is considerable uncertainty as to the site of the impurity ion.     

广西大化透闪石玉的发现及初步研究

利用偏光显微镜、X射线衍射、电子探针、扫描电镜、红外光谱等测试方法,对广西大化新发现的透闪石玉进行了宝玉石特征、矿物组成及结构构造的研究,结果表明大化透闪石玉的主要矿物组成为透闪石,主要结构与和田玉基本一致,其宝石特征已经达到玉石级并已制作成雕件饰品加工销售。     

异极矿热相变过程的高温原位拉曼光谱

利用高温拉曼光谱技术,对异极矿进行了原位拉曼光谱的测试和研究。结果表明,异极矿加热至800 K时,与结晶水(H₂O)中O-H伸缩振动对应的3 470 cm^-1特征拉曼谱峰消失,但标志硅酸盐骨架[Si₂O^₇] (Q1)结构的特征谱峰926 cm^-1未受影响,表明结晶水的丢失并不影响异极矿的整体结构。当加热至1 050 K,反映结构水O-H伸缩振动的特征峰3 580 cm^-1消失,与Q1结构单元Si-Onb对称伸缩振动相对应的特征峰926 cm^-1强度逐渐减小,并出现与Q0相对应的852.4 cm^-1特征峰。这表明加热到1 050 K时,异极矿开始出现相变。当升温达1 100 K以上,结构水(OH)的特征谱峰(3 580 cm^-1)消失,与Si-Onb对称伸缩振动对应的特征拉曼谱峰变为855 cm^-1,这标志着异极矿原有的Q1结构已完全转变为硅锌矿的Q0结构 ([SiO₄]结构),也就是说异极矿已完成向硅锌矿的转变。