Disposal of wastewater containing Congo Red by synthesizing layer double hydroxide in-situ

Based on the principle of synthesis, a new method was put forward to dispose Congo Red anion-containing dyestuff from wastewater and its feasibility was also examined. The principle of the method is described as follows： Mg^2＋ and Al^3＋ are hydrolyzed to form Mg/Al-LDH by adding Mg^2＋, Al^3＋ and NaOH in wastewater containing anion dyestuff, which is selectively intercalated with the interlayer of LDH in order to balance positive structural charge. While Mg^2＋ and Al^3＋ are co-precipitated to form LDH, the anion dyestuff in wastewater will be removed by LDH synthesized in-situ, as is confirmed by X-ray diffraction analysis of settlings and chemical analysis of aqueous samples. In this work, we studied the influence of Mg/Al mole ratio, pH value, time and temperature of reaction on the removal of anion dyestuff and the use of Mg and Al. The experimental results showed the maximum removal efficiency of anion dyestuff could be attained when pH value was 9.0, and Mg/Al mol ratio was 2 ： 1, reaction duration was 2 hours, and the effect of temperature was not remarkable, and the removal efficiency could reach 100%. Meanwhile, the Mg and Al added could be made good use of. This technology has the advantage of extraordinary efficiency of wastewater disposal.     

Aluminum substitution mechanisms in perovskite-type MgSiO<Subscript>3</Subscript>: an investigation by Rietveld analysis

Al-containing MgSiO₃ perovskites of four different compositions were synthesized at 27 GPa and 1,873 K using a Kawai-type high-pressure apparatus: stoichiometric compositions of Mg_0.975Si_0.975Al_0.05O₃ and Mg_0.95Si_0.95Al_0.10O₃ considering only coupled substitution Mg²⁺ + Si⁴⁺ = 2Al³⁺, and nonstoichiometric compositions of Mg_0.99Si_0.96Al_0.05O_2.985 and Mg_0.97Si_0.93Al_0.10O_2.98 taking account of not only the coupled substitution but also oxygen vacancy substitution 2Si⁴⁺ = 2Al³⁺ + V_O¨. Using the X-ray diffraction profiles, Rietveld analyses were performed, and the results were compared between the stoichiometric and nonstoichiometric perovskites. Lattice parameter–composition relations, in space group Pbnm, were obtained as follows. The a parameters of both of the stoichiometric and nonstoichiometric perovskites are almost constant in the X _Al range of 0–0.05, where X _Al is Al number on the basis of total cation of two (X _Al = 2Al/(Mg + Si + Al)), and decrease with further increasing X _Al. The b and c parameters of the stoichiometric perovskites increase linearly with increasing Al content. The change in the b parameter of the nonstoichiometric perovskites with Al content is the same as that of the stoichiometric perovskites within the uncertainties. The c parameter of the nonstoichiometric perovskites is slightly smaller than that of the stoichiometric perovskites at X _Al of 0.10, though they are the same as each other at X _Al of 0.05. The Si(Al)–O1 distance, Si(Al)–O1–Si(Al) angle and minimum Mg(Al)–O distance of the nonstoichiometric perovskites keep almost constant up to X _Al of 0.05, and then the Si(Al)–O1 increases and both of the Si(Al)–O1–Si(Al) angle and minimum Mg(Al)–O decrease with further Al substitution. These results suggest that the oxygen vacancy substitution may be superior to the coupled substitution up to X _Al of about 0.05 and that more Al could be substituted only by the coupled substitution at 27 GPa. The Si(Al)–O1 distance and one of two independent Si(Al)–O2 distances in Si(Al)O₆ octahedra in the nonstoichiometric perovskites are always shorter than those in the stoichiometric perovskite at the same Al content. These results imply that oxygen defects may exist in the nonstoichiometric perovskites and distribute randomly.     

贵州水银洞卡林型金矿床首次发现大量次显微-显微可见自然金颗粒

在贵州水银洞卡林型金矿床原生富矿石的一条含砷黄铁矿细脉中发现有100余粒次显微-显微自然金颗粒(0.1~6μm),并具有清晰的显微岩相学结构。提出了该类型金矿次显微-显微可见自然金颗粒的形成过程可能与含Au热液-岩石相互作用过程中含Fe碳酸盐矿物溶解释放Fe的大量硫化物化而导致热液中Au的过饱和有关,含Fe碳酸盐赋矿围岩是形成高品位大型卡林型金矿床最重要的控制因素之一。     

即时合成Zn-Mg-Al层状双氢氧化物处理含Zn2+废水实验研究

在模拟含Zn2 废水中加入Mg2 和Al3 ,以NaOH为沉淀剂,研究金属盐水解即时合成层状双氢氧化物(LDH)去除Zn2 的可行性。详细探讨了体系终点pH值、配料中Mg2 /Zn2 摩尔比值及反应温度和时间对Zn2 去除率的影响,结合X射线衍射分析(XRD)探讨了Zn2 去除机理,并与化学沉淀法进行了比较。结果表明,实验条件下只有pH值显著影响Zn2 去除率(p<0.05),在9.0~11.0范围内去除效果最佳,达99%以上。通过XRD分析结合即时合成法特点,废水中Zn2 主要是在晶体生成阶段以Zn-Mg-Al三元LDH化合物形式被去除的。与化学沉淀法相比,即时合成法效果更好,适用pH值范围更广,用来处理含Zn2 废水更具优势。     

Analysis of cation distribution in the octahedral sheet of dioctahedral 2:1 phyllosilicates by using inverse Monte Carlo methods

An inverse Monte Carlo (MC) method was developed to determine the distribution of octahedral cations (Al³⁺, Fe³⁺, and Mg²⁺) in bentonite illite–smectite (I–S) samples (dioctahedral 2:1 phyllosilicates) using FT–IR and ²⁷Al MAS NMR spectroscopies. FT–IR allows determination of the nature and proportion of different cation pairs bound to OH groups measuring the intensities of OH-bending bands. ²⁷Al MAS NMR data provide information about cation configuration because ²⁷Al MAS NMR intensity depends on Fe distribution. MC calculations based on FT–IR data alone show Fe segregation by short-range ordering (Fe clusters within 9 to 15?Å from a given Fe atom). Fe segregation increases with illite proportion. MC calculations based on IR and ²⁷Al NMR simultaneously yield similar configurations in which Fe clusters are smaller. The latter calculations fail to build appropriate cation distributions for those samples with higher number of illite layers and significant Fe content, which is indicative of long-range Fe ordering that cannot be detected by FT–IR and ²⁷Al MAS NMR. The proportion of Mg–Mg pairs is negligible in all samples, and calculations, in which the number of Mg atoms, as second neighbours, is minimised, create appropriate configurations.     

The crystal and melt structure of spinel and alumina at high temperature: An in-situ XANES study at the Al and Mg K-edge

We present structural information obtained on spinel and alumina at high temperature (298-2400 K) using in-situ XANES at the Mg and Al K-edges. For spinel, ^[4](Al_x,Mg_1−x)^[6](Al_2−x,Mg_x)O_4, with increasing temperature, a substitution of Mg by Al and Al by Mg in their respective sites is observed. This substitution corresponds to an inversion of the Mg and Al sites. There is a significant change in the Al K-edge spectra between crystal and liquid, which can be attributed to a change of the ^[6]Al normally observed in corundum at room temperature, to a mixture of ^[6]Al-^[4]Al in the liquid state. This conclusion is in good agreement with previous ²⁷Al NMR experiments. Furthermore, both experiments at the Al and Mg K-edges are in good agreement with XANES calculation made using FDMNES code.     

臭氧化含苯酚污水投加水镁石沉淀出草酸镁的实验研究

本文通过两组不同水镁石-苯酚投料比的实验,研究固体沉淀物与水质变化的关系。实验显示,水镁石解离出的Mg²⁺与苯酚降解的中间产物能形成难溶盐,并发生沉淀分离,促进含苯酚废水臭氧化降解的效率。当苯酚的初始浓度为47 g/L,初始碳镁原子比(C/Mg)为30时,经3小时充分臭氧化曝气后,投加的水镁石全部耗尽。XRD、TG/DSC结果显示新形成的沉淀物为草酸镁。反应终点的pH值在4以下,TOC去除率为40%。当体系的初始C/Mg(原子比)为1,苯酚的初始浓度为1.5 g/L时,同样的臭氧化曝气过程体系残留的沉淀物仍是水镁石。反应终点的pH值在10左右,TOC去除率为92.8%。研究证明,苯酚臭氧化过程也是体系酸化的过程,至少在高C/Mg比条件下新生的质子能与水镁石解离出的羟基中和,水镁石解离出的Mg²⁺可与草酸根结合沉淀出草酸镁。     

On local structural changes in lizardite-1T: {Si4+/Al3+}, {Si4+/Fe3+}, [Mg2+/Al3+], [Mg2+/Fe3+] substitutions

Geometrical changes induced by cation substitutions {Si⁴⁺/Al³⁺}[Mg²⁺/Al³⁺], {2Si⁴⁺/2Al³⁺} [2Mg²⁺/2Al³⁺], {Si⁴⁺/Fe³⁺} [Mg²⁺/Al³⁺] or [Mg²⁺/Fe³⁺], where {} and [] indicate tetrahedral and octahedral sheet in lizardite 1T, are studied by ab-initio quantum chemistry calculations. The majority of the models are based on the chemical compositions reported for various lizardite polytypes with the amount of Al in the tetrahedral sheets reported to vary from 3.5% to 8% in the 1T and 2H ₁, up to ~30% in the 2H ₂ polytype. Si⁴⁺ by Fe³⁺ substitution in the tetrahedral sheet with an Al³⁺ (Fe³⁺) in the role of a charge compensating cation in the octahedral sheet is also examined. The cation substitutions result in the geometrical changes in the tetrahedral sheets, while the octahedral sheets remain almost untouched. Substituted tetrahedra are tilted and their basal oxygens pushed down from the plane of basal oxygens. Ditrigonal deformation of tetrahedral sheets depends on the substituting cation and the degree of substitution.     

Compositional effects on element partitioning between Mg-silicate perovskite and silicate melts

High-pressure melting experiments were performed at ~26 GPa and ~2,200–2,400°C on synthetic peridotite compositions with varying FeO and Al₂O₃ contents and on a synthetic CI chondrite analogue composition. Peridotite liquids show a crystallisation sequence of ferropericlase (Fp) followed down temperature by Mg-silicate perovskite (MgPv) + Fp, which contrasts a sequence of MgPv followed by MgPv + Fp observed in the chondritic composition. The difference in crystallisation sequence is a consequence of the different bulk Mg/Si ratios. MgPv/melt partition coefficients for major, minor and trace elements were determined by electron microprobe and secondary ion mass spectrometry. Partition coefficients of tri- and tetravalent elements increase with increasing Al concentration in MgPv. A lattice strain model indicates that Al³⁺ substitutes predominantly onto the Si-site in MgPv, whereas most elements substitute onto the Mg-site, which is consistent with a charge-compensating coupled substitution mechanism. MgPv/melt partition coefficients for Mg (D_Mg) and Si (D_Si) are related to the melt Mg/Si ratio such that D_Si becomes lower than D_Mg at low Mg/Si melt ratios. We use a crystal fractionation model, based on upper mantle refractory lithophile element ratios, to constrain the amount of MgPv and Ca-silicate perovskite (CaPv) that could have fractionated during a Hadean magma ocean event and could still be present as a chemically distinct heterogeneity in the lower mantle today. We show that a fractionated crystal pile composed of 96% MgPv and 4% CaPv could comprise up to 13 wt% of the entire mantle.     

Zoned clinopyroxenes from the volcanic rocks of almopia (Voras Mts), Central Macedonia,Greece

Summary In the zoned clinopyroxene phenocrysts from the volcanic rocks of Almopia the Mg/Fe ratio and the contents of Mn, and mostly of Na, increase from the core towards the rim of the crystals, whereas the Fe³⁺/Fe²⁺ ratio, and in many cases the contents of Ca, decrease. On the contrary, the content of Si decreases from inside outwards or remains almost constant whereas Al and Ti increase.The high Ca-content of the clinopyroxenes, low Ti, and limited Fe-enrichment, with a trend from Ca_43.3: Mg_47.0: (Fe + Mn)_9.7 to Ca_46.6: Mg_42.2: (Fe + Mn)_11.2, illustrate the shoshonitic to cale-alkaline nature of the parental magma.The composition of the clinopyroxenes indicates that, of all possible controlling factors, the high water-vapour pressure is considered to play an important role for the Al^IV fluctuations during the crystallization.

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Zonierte klinopyroxene der vulkanite von almopia (Voras-Gebirge), Zentral-Mazedonien, Griechenland

Zusammenfassung Bei den zonierten Klinopyroxeneinsprenglingen der Vulkanite von Almopia nehmen das Mg/Fe-Verhältnis und die Gehalte an Mn und meistens an Na in den einzelnen Zonen vom Kern zum Rand zu, während das Fe³⁺/Fe²⁺-Verhältnis, und in vielen Fällen die Gehalte an Ca, abnehmen. Im Gegensatz dazu nimmt der Gehalt an Si von innen nach außen ab oder bleibt fast konstant, während Al und Ti zunehmen.Der hohe Ca-Gehalt und gleichzeitig niedrige Ti-Gehalt der Klinopyroxene, zusammen mit ihrer begrenzten Fe-Anreicherung und einem Trend von Ca_43.3: Mg_47.0: (Fe + Mn)_9.7 bis Ca_46.6: Mg_42.2: (Fe + Mn)_11.2 weisen auf die shoshonitische bis kalk-alkalische Natur des Stammagmas hin. Die Zusammensetzung der Klinopyroxene weist darauf hin, daß der hohe Wasserdampfdruck im Magma auch eine wichtige Rolle für Schwankungen im Al^IV-Gehalt während der Kristallisation darstellt.

     

Multiple origins of clinopyroxenes in alkali basaltic rocks

Geochemical and textural data on clinopyroxenes in individual alkali basaltic flows from provinces in eastern Australia and the Massif Central can be used to differentiate four different modes of origin (three at high pressure) for these clinopyroxenes. Many single flows from the two provinces contain clinopyroxenes of three, or even four, of these origins. Rare flows contain core clinopyroxene with overgrowths of clinopyroxenes of two distinct generation. Each of the overgrowth is compositionally analogous to clinopyroxenes occurring in xenoliths or as discrete crystals in the same host lava. Such rimming relationships provide evidence that the host magma has undergone high pressure crystallisation and confirm that some xenoliths and megacrysts are cognate. With decreasing pressure the major changes in clinopyroxene chemistry are an increase in the ratio Al^lv/Al^vi, a linear increase of atomic proportions of Ti and Al with decreasing Si, and an increase in the Ti: (100 Mg/(Mg + Σ Fe)) ratio of the pyroxenes. Al₂O₂ wt, % is an unreliable potential geobarometric indicator; consideration of tetrahedral and octahedral site occupancies by Al (Al^lv/Al^vl ratio) is necessary. High-pressure fractionation dominated by clinopyroxene is postulated for some basaltic-composition, resulting in SiO₂ depletion, alkali enrichment and decrease in the Mg/(Mg + Fe²⁺) value of the host magma.     

Thermochemical study Mg–Fe amphiboles

The paper presents data on the thermochemical study (high-temperature melt calorimetry in a Tian–Calvet microcalorometer) of two natural Mg–Fe amphiboles: anthophyllite Mg_2.0(Mg_4.8Fe_0.2 ²⁺)[Si_8.0O₂₂](OH)₂ from Kukh-i-Lal, southwestern Pamirs, Tajikistan, and gedrite Na_0.4Mg_2.0(Mg_1.7Fe_0.2 ²⁺Al_1.3)[Si_6.3Al_1.7O₂₂](OH)₂ from the Kola Peninsula, Russia. The enthalpy of formation from elements is obtained as–12021 ± 20 kJ/mol for anthophyllite and as–11545 ± 12 kJ/mol for gedrite. The standard entropy, enthalpy, and Gibbs energy of formation are evaluated for Mg–Fe amphiboles of theoretical composition.     

Chemical composition and species attribution of tourmalines from a rare-metal pegmatite vein with scapolite, Sangilen Upland, Tuva

A detailed study of the chemical composition and substitutions in calcium tourmalines from a scapolite-bearing rare-metal pegmatite vein from the Sol’bel’der River basin has shown that their species attribution is determined by occupancy of octahedral site Y. The composition of the yellow tourmaline most abundant in the central part of the pegmatite bodyis rather constant and characterized by the ideal formula Ca(Mg₂Li)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃F. Variations in the chemical composition of zonal tourmaline crystals from the contact part of the pegmatite are controlled by abrupt change in the chemical medium during their formation. The yellow cores of these crystals are close in composition to tourmaline from the central part of the pegmatite vein. The Mg content abruptly decreases toward the crystal margin: Mg²⁺ → Fe²⁺, 2Mg²⁺ → Li⁺ + Al³⁺, and Mg²⁺ + OH → Al³⁺ + O²⁻. The composition of dark green marginal zones in tourmaline is characterized by the ideal formula Ca(Al_1.5Li_1.5)Al₆(Si₆O₁₈)(BO₃)₃ (OH₂O)(F). The results indicate specific formation conditions of pegmatite. The crystallochemical formulas of the studied tourmalines allow us to regard them as new mineral species in the tourmaline group.     

Pseudosinhalite: discovery of the hydrous MgAl-borate as a new mineral in the Tayozhnoye, Siberia, skarn deposit

After its initial synthesis as the new compound Mg₂Al₃B₂O₉(OH) (Daniels et al. 1997) pseudosinhalite has now been discovered as a new mineral. It occurs, together with hydrotalcite, as a replacement product of sinhalite, MgAlBO₄, in an impure marble of the contact metasomatic iron boron deposit of Tayozhnoye in the Aldan Shield of Siberia. Its chemical composition determined by electron microprobe is (wt%): Al₂O₃ 46.88; MgO 25.12; FeO 1.99; B₂O₃ (calculated) 21.75; H₂O (calculated) 2.81 giving a total of 98.55 and leading to the empirical formula (Mg_2.00 Fe²⁺ _0.09)_Σ=2.09 Al_2.94 B₂O₉(OH). The small deviation from the ideal stoichiometry with (Mg?+?Fe²⁺):Al?≠?2:3 may be caused by either solid solution towards, or submicroscopic interlayering with lamellae of, the structurally similar mineral sinhalite. The underlying substitution involving also B and H would be (Mg?+?Fe)+?B=Al+2H. Pseudosinhalite is monoclinic, space group P2₁/c, with a=7.49(1), b=4.33(1), c=9.85(2) Å; β=110.7(1)°; V?=?299(1) ų; Z?=?2. Calculated density is 3.508?g/cm³. Pseudosinhalite is colourless with white streak and has a vitreous lustre. It is transparent; no fluorescence was detected. There is no cleavage and parting; fractures are concoidal. Optical constants could not be measured properly due to polysynthetic microtwinning, but α<1.72<γ. For synthetic pseudosinhalite α=1.691(1); β=1.713(1); γ=1.730(1); Δ=0.039; 2?V=80°. The temperature of pseudosinhalite formation was below about 400?°C at low pressures and with a hydrous, CO₂-bearing fluid participating in the reaction.     

The crystal structure of cualstibite-1M (formerly cyanophyllite), its revised chemical formula and its relation to cualstibite-1T

The crystal structure of the rare secondary mineral cualstibite-1M (formerly cyanophyllite), originally reported to have the chemical formula 10CuO·2Al₂O₃·3Sb₂O₃·25H₂O and orthorhombic symmetry, was solved from single-crystal intensity data (Mo-Kα X-radiation, CCD area detector, 293 K, 2θ_max?=?80) collected on a twinned crystal containing very minor Mg. The mineral is monoclinic, P2₁/c (no. 14), with a?=?9.938(1), b?=?8.890(1), c?=?5.493(1) Å, β?=?102.90(1)°, V?=?473.05(11) ų; R1(F)?=?0.0326. All crystals investigated turned out to be non-merohedric twins. The atomic arrangement has a distinctly layered character. Brucite-like sheets composed of two [4?+?2]-coordinated (Cu,Al,Mg) sites are linked by weak hydrogen-bonding (O···O?~?2.80 Å) to isolated regular Sb(OH)₆ octahedra (<Sb-O>?=?1.975 Å). The layered, pseudotrigonal character explains the perfect cleavage and the proneness to twinning. The Sb site is fully occupied and the two (Cu,Al,Mg) sites have occupancies of Cu_0.79Al_0.17Mg_0.04 and Cu_0.72Al_0.23Mg_0.05. The Cu-richer site shows a slightly stronger Jahn-Teller-distortion. The resulting empirical formula, which necessitates a H₂O-for-OH substitution to obtain charge balance, is (Cu_2.23Al_0.63Mg_0.14)(OH)_5.63(H₂O)_0.37[Sb⁵⁺(OH)₆]. The ideal chemical formula is (Cu,Al)₃(OH)₆[Sb⁵⁺(OH)₆], with Cu:Al = 2:1. The structure is closely related to those of trigonal cualstibite-1T [Cu₂AlSb(OH)₁₂, P-3, with ordered Cu-Al distribution in the brucite sheets], and its Zn analogue zincalstibite-1T [Zn₂AlSb(OH)₁₂]. Cualstibite-1M and cualstibite-1T are polytypes and, together with zincalstibite-1T, zincalstibite-9R and omsite, belong to the cualstibite group within the hydrotalcite supergroup, which comprises all natural members of the large family of layered double hydroxides (LDH).     

水滑石对水溶性染料活性深蓝ST-2GLN脱色性能研究

研究了水滑石(LDH)及其焙烧产物(LDO)吸附脱除水溶液中活性深蓝ST-2GLN的性能。考察了pH值、吸附剂投加量、时间等因素对吸附的影响。结果表明:LDH及LDO对活性深蓝ST-2GLN染料具有良好的脱除效果,室温下,1 g/L的LDH和0.5 g/L的LDO对浓度为100 mg/L的染料的脱色率分别达到96.11%和98.58%。pH值是影响吸附能力的关键因素,吸附剂对溶液pH值有一定缓冲作用。LDH及LDO对活性深蓝ST-2GLN吸附结果均符合Langmuir吸附等温式。饱和吸附后的LDH用高温热解法再生,再生产物吸附性能良好,随再生次数增多,脱色率下降。     

Thermochemical study of Mg–Fe chlorites

The thermochemical study of two natural trioctahedral Mg–Fe chlorites—clinochlores was carried out using high-temperature melt solution calorimetry with a Tian–Calvet microcalorimeter. The enthalpies of formation of clinochlores of compositions (Mg_4.9Fe _0.3 ²⁺ Al_0.8)[Si_3.2Al_0.8O₁₀](OH)₈ (–8811 ± 12 kJ/mol) and (Mg_4.3Fe _0.7 ²⁺ Al_1.0)[Si_3.0Al_1.0O₁₀](OH)₈ (–8696 ± 13 kJ/mol) from elements were determined. The values of the standard entropies and the Gibbs energies of formation of the studied natural minerals as well as thermodynamic properties of Mg–Fe chlorites of theoretical composition were estimated.     

The compositional variation of synthetic sodic amphiboles at high and ultra-high pressures

Sodic amphiboles in high pressure and ultra-high pressure (UHP) metamorphic rocks are complex solid solutions in the system Na₂O–MgO–Al₂O₃–SiO₂–H₂O (NMASH) whose compositions vary with pressure and temperature. We conducted piston-cylinder experiments at 20–30?kbar and 700–800?°C to investigate the stability and compositional variations of sodic amphiboles, based on the reaction glaucophane=2jadeite+talc, by using the starting assemblage of natural glaucophane, talc and quartz, with synthetic jadeite. A close approach to equilibrium was achieved by performing compositional reversals, by evaluating compositional changes with time, and by suppressing the formation of Na-phyllosilicates. STEM observations show that the abundance of wide-chain structures in the synthetic amphiboles is low. An important feature of sodic amphibole in the NMASH system is that the assemblage jadeite–talc?±?quartz does not fix its composition at glaucophane. This is because other amphibole species such as cummingtonite (Cm), nyböite (Nyb), Al–Na-cummingtonite (Al–Na-Cm) and sodium anthophyllite (Na-Anth) are also buffered via the model reactions: 3cummingtonite?+?4quartz?+?4H₂O=7talc, nyböite?+?3quartz=3jadeite?+?talc, 3Al–Na-cummingtonite + 11quartz + 2H₂O=6jadeite + 5talc, and 3 sodium anthophyllite?+?13quartz?+?4H₂O=3 jadeite + 7talc. We observed that at all pressures and temperatures investigated, the compositions of newly grown amphiboles deviate significantly from stoichiometric glaucophane due to varying substitutions of Al^IV for Si, Mg on the M(4) site, and Na on the A-site. The deviation can be described chiefly by two compositional vectors: [Na^AAl^IV]<=>[□^ASi] (edenite) toward nyböite, and [Na^(M4)Al^VI]<=>[Mg^(M4)Mg^VI] toward cummingtonite. The extent of nyböite and cummingtonite substitution increases with temperature and decreases with pressure in the experiments. Similar compositional variations occur in sodic amphiboles from UHP rocks. The experimentally calibrated compositional changes therefore may prove useful for thermobarometric applications.     

Shear viscosities of CaO-Al2O3-SiO2 and MgO-Al2O3-SiO2 liquids: Implications for the structural role of aluminium and the degree of polymerisation of synthetic and natural aluminosilicate melts

The shear viscosity of 66 liquids in the systems CaO-Al₂O₃-SiO₂ (CAS) and MgO-Al₂O₃-SiO₂ (MAS) have been measured in the ranges 1-10⁴ Pa s and 10⁸-10¹² Pa s. Liquids belong to series, nominally at 50, 67, and 75 mol.% SiO₂, with atomic M²⁺/(M²⁺+2Al) typically in the range 0.60 to 0.40 for each isopleth. In the system CAS at 1600°C, viscosity passes through a maximum at all silica contents. The maxima are clearly centered in the peraluminous field, but the exact composition at which viscosity is a maximum is poorly defined. Similar features are observed at 900°C. In contrast, data for the system MAS at 1600°C show that viscosity decreases with decreasing Mg/(Mg + 2Al) at all silica contents, but that a maximum in viscosity must occur in the field where Mg/2Al >1. On the other hand, the viscosity at 850°C increases with decreasing Mg/(Mg + 2Al) and shows no sign of reaching a maximum, even for the most peraluminous composition studied. The data from both systems at 1600°C have been analysed assuming that shear viscosity is proportional to average bond strength and considering the equilibrium:

Al^[4]-(Mg,Ca)_0.5⇔(Mg,Ca)_0.5-NBO+Al_XS     

Characterization of NH4-phlogopite (NH4) (Mg3) [AlSi3O10] (OH)2 and ND4-phlogopite (ND4) (Mg3) [AlSi3O10] (OD)2 using IR spectroscopy and Rietveld refinement of XRD spectra

 A synthesis technique is described which results in >99% pure NH₄-phlogopite (NH₄) (Mg₃) [AlSi₃O₁₀] (OH)₂ and its deuterium analogue ND₄-phlogopite (ND₄) (Mg₃) [AlSi₃O₁₀] (OD)₂. Both phases are characterised using both IR spectroscopy at 298 and 77 K as well as Rietveld refinement of their X-ray powder diffraction pattern. Both NH₄ ⁺ and ND₄ ⁺ are found to occupy the interlayer site in the phlogopite structure. Absorption bands in the IR caused by either NH₄ ⁺ or ND₄ ⁺ can be explained to a good approximation using T_d symmetry as a basis. Rietveld refinement indicates that either phlogopite synthesis contains several mica polytypes. The principle polytype is the one-layer monoclinic polytype (1M), which possesses the space group symmetry C2/m. The next most common polytype is the two-layer polytype (2M ₁ ) with space group symmetry C2/c. Minor amounts of the trigonal polytype 3T with the space group symmetry P3₁12 were found only in the synthesis run for the ND₄-phlogopite. Electron microprobe analyses indicate that NH₄-phlogopite deviates from the ideal phlogopite composition with respect to variable Si/Al and Mg/Al on both the tetrahedral and octahedral sites, respectively, due to the Tschermaks substitution ^VIMg²⁺+^IVSi⁴⁺↔^VIAl³⁺+^IVAl³⁺ and with respect to vacancies on the interlayer site due to the exchange vector ^XII(NH₄)⁺+^IVAl³⁺↔^XII□+^IVSi⁴⁺. Received: 30 August 1999 / Accepted: 2 October 2000