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1.
Thermodynamic analysis of the system Na2O-K2O-CaO-Al2O3-SiO2-H2O-F2O–1 provides phase equilibria and solidus compatibilities of rock-forming silicates and fluorides in evolved granitic systems and associated hydrothermal processes. The interaction of fluorine with aluminosilicate melts and solids corresponds to progressive fluorination of their constituent oxides by the thermodynamic component F2O–1. The chemical potential (F2O–1) buffered by reaction of the type: MOn/2 (s)+n/2 [F2O–1]=MFn (s, g) where M=K, Na, Ca, Al, Si, explains the sequential formation of fluorides: carobbiite, villiaumite, fluorite, AlF3, SiF4 as well as the common coexistence of alkali- and alkali-earth fluorides with rock-forming aluminosilicates. Formation of fluorine-bearing minerals first starts in peralkaline silica-undersaturated, proceeds in peraluminous silica-oversaturated compositions and causes progressive destabilization of nepheline, albite and quartz, in favour of villiaumite, cryolite, topaz, chiolite. Additionally, it implies the increase of buffered fluorine solubilities in silicate melts or aqueous fluids from peralkaline silica-undersaturated to peraluminous silica-oversaturated environments. Subsolidus equilibria reveal several incompatibilities: (i) topaz is unstable with nepheline or villiaumite; (ii) chiolite is not compatible with albite because it only occurs only at very high F2O–1 levels. The stability of topaz, fluorite, cryolite and villiaumite in natural felsic systems is related to their peralkalinity (peraluminosity), calcia and silica activity, and linked by corresponding chemical potentials to rock-forming mineral buffers. Villiaumite is stable in strongly peralkaline and Ca-poor compositions (An<0.001). Similarly, cryolite stability requires coexistence with nearly-pure albite (An<2). Granitic rocks with Ca-bearing plagioclase (An>5) saturate with topaz or fluorite. Crystallization of topaz is restricted to peraluminous conditions, consistent with the presence of Li-micas or anhydrous aluminosilicates (cordierite, garnet, andalusite). Fluorite is predicted to be stable in peraluminous biotite granites, amphibole-, clinopyroxene- or titanite-bearing calc-alkaline suites as well as in peralkaline granitic and syenitic rocks. Fluorine concentrations in felsic melts buffered by the coexistence of F-bearing minerals and feldspars increase from peralkaline through metaluminous to mildly peraluminous compositions. At low-temperature conditions, the hydrothermal evolution of peraluminous granitic and greisen systems is controlled by white mica-feldspar-fluoride equilibria. With decreasing temperature, topaz gradually breaks down via: (i) (OH)F–1 substitution and fluorine transfer to fluorite by decalcification of plagioclase below 600 °C, (ii) formation of muscovite and additional fluorite at 475–315 °C, and (iii) formation of paragonite and cryolite, consuming F-rich topaz and albite below 315 °C. These equilibria explain the absence of magmatic fluorite in Ca-bearing topaz granitic rocks; its abundance in hydrothermal rocks is due to: (i) closed-system defluorination of topaz, (ii) open-system decalcification of plagioclase or (iii) hydrolytic alteration. These results provide a complete framework for the investigation of fluorine-bearing mineral stabilities in felsic igneous suites.Electronic Supplementary Material Supplementary material is available in the online version of this article at . A link in the frame on the left on that page takes you directly to the supplementary material.Editorial responsibility: T.L. Grove 相似文献
2.
Mario Tribaudino Fabrizio Nestola Marco Bruno Tiziana Boffa Ballaran Christian Liebske 《Physics and Chemistry of Minerals》2008,35(5):241-248
The high temperature volume and axial parameters for six C2/c clinopyroxenes along the NaAlSi2O6–NaFe3+Si2O6 and NaAlSi2O6–CaFe2+Si2O6 joins were determined from room T up to 800°C, using integrated diffraction profiles from in situ high temperature single crystal data collections. The thermal
expansion coefficient was determined by fitting the experimental data according to the relation: ln(V/V
0) = α(T − T
0). The thermal expansion coefficient increases by about 15% along the jadeite–hedenbergite join, whereas it is almost constant
between jadeite and aegirine. The increase is related to the Ca for Na substitution into the M2 site; the same behaviour was
observed along the jadeite–diopside solid solution, which presents the same substitution at the M2 site. Strain tensor analysis
shows that the major deformation with temperature occurs in all samples along the b axis; on the (010) plane the higher deformation occurs in jadeite and aegirine at a direction almost normal to the tetrahedral–octahedral
planes, and in hedenbergite along the projection of the longer M2–O bonds. The orientation of the strain ellipsoid with temperature
in hedenbergite is close to that observed with pressure in pyroxenes. Along the jadeite–aegirine join instead the high-temperature
and high-pressure strain are differently oriented. 相似文献
3.
通过密度泛函理论模拟了H_2O_2和SO_2气体在矿物氧化物(α-Fe_2O_3)表面上的非均相反应,研究了H_2O_2和SO_2在α-Fe_2O_3(001)表面的吸附机制和氧化机制。研究结果表明,SO_2、H_2O_2均在α-Fe_2O_3(001)表面通过Fe原子进行吸附,H_2O_2相比于SO_2优先吸附在α-Fe_2O_3(001)表面,且H_2O_2在表面的赋存形式趋向于两个·OH形式吸附。通过二者共吸附的局域态密度、差分电荷密度、Mulliken电荷布局分析结果发现,SO_2和H_2O_2的共吸附形式是通过H_2O_2产生的·OH吸附在α-Fe_2O_3(001)表面,同时SO_2被H_2O_2产生的·OH氧化[S(SO_2)-电荷布局:0. 79 e→1. 32 e; O(H_2O_2)-电荷布局:-0. 77 e→-1. 11 e]形成·OH+SO_2团簇。模拟结果表明大气微量气体H_2O_2能够在矿物氧化物表面介导SO_2吸附并促进SO_2的转化,为理解H_2O_2在大气中非均相氧化SO_2的反应过程提供了理论依据。 相似文献
4.
西大别造山带红安高压榴辉岩主要矿物为石榴石、绿辉石、冻蓝闪石、石英和绿帘石,有时可见蓝闪石、多硅白云母和钠云母。石榴石具有生长环带且边缘成分变化大,可分为代表峰期的Ⅰ型边（XMg高、Grs低）和受退变质改造的Ⅱ型边（XMg低、Grs高）。石榴石内蓝闪石包体发育冻蓝闪石退变边,说明包体不能完全反映进变质条件。基质绿辉石比包体绿辉石Jd含量低,在一个晶体内成分有明显变化和沿解理缝发育冻蓝闪石,显示峰后绿辉石有成分变化和退变质改造。基质中冻蓝闪石晶体较大,核部见有蓝闪石残留,说明二者有成因联系。冻蓝闪石和绿辉石都发育后成合晶结构,石榴石有韭闪石的反应冠状体。在THERMOCALC程序计算的P-T视剖面图中,石榴石Ⅰ型边反映的峰期P-T条件为2.4~2.6GPa、570~585℃,和基质中多硅白云母Si含量等值线限定范围一致,对应硬柱石蓝闪石榴辉岩组合。石榴石Ⅱ型边P-T范围为1.9~2.4GPa、530~570℃,低于峰期条件。在可能的峰后降压过程中,岩石先后主要经历了硬柱石脱水生成绿帘石和蓝闪石、绿辉石退变为冻蓝闪石的反应阶段。绿辉石、冻蓝闪石发育的后成合晶说明晚期退变过程缺乏流体,石榴石的韭闪石冠状体也可能在该阶段产生,都受局部成分域控制。红安高压榴辉岩中各矿物与成分代表不同变质阶段,称其为冻蓝闪石榴辉岩只是对现有主要组成矿物的描述,不是基于共生关系的严格岩石学命名。 相似文献
5.
6.
盐渍土的盐性是决定盐渍土地区工程治理方案所必须考虑的一个重要因素。目前盐性鉴定的方法多局限于确定单一化合物晶体,但对于自然界常是两种以上化合物共存的情况,分析鉴定还不多见。本文针对试验配制的硫酸钠、氯化钠共存的水溶液在25℃和10℃等温条件下,采用正交偏光显微镜、差热分析仪和X—衍射仪,对其固相晶体进行鉴定识别并得到如下结论: 1.在硫酸钠、氯化钠固相共存的条件下,它们各自仍保留原化合物的部分物理、热学和光学特性,仍能采用差热分析、偏光显微镜、X—衍射的方法对其进行鉴别。 2.在正交偏光显微镜下,这两种化合物共存的固相晶型与单一化合物的固相晶型光学性质略有不同,但仍存有单一化合物晶型的部分光学性质,由此能定性地进行固相鉴别。 3.利用差热分析仪和X 衍射试验表明,这两种化合物共存的固相吸热峰值、衍射峰值与单一化合物固相吸热峰值和衍射峰值有所变化,但仍有其一定的变化规律并能以此定性和半定量的鉴别哪种化合物存在与否及两者的近似比例。 相似文献
7.
世界上很多海域中的现代碳酸盐沉积正在形成,如巴哈马滩、美国的佛罗里达湾、古巴的巴塔诺湾、中东的波斯湾等地,以及丹麦的某些近海地区。产于这些海域中的现代碳酸盐沉积物,其矿物组成主要是文石,其次为镁方解石,纯方解石较少,现代白云石沉积更为少见。我国的现代碳酸盐沉积见于南海诸岛及海南岛的沿海地带。作者曾利用粉晶照相鉴定了采自我国南海二十余种珊瑚、瓣鳃类、腹足类、有孔虫等现代海相生物壳体的物相,发现除有孔虫和海胆壳是由镁方解石构成外,其余生物壳体皆由文石构成。 相似文献
8.
采用等温溶解平衡法研究了288K时Li+, Mg2+//SO2-4, B4O2-7- H2O四元体系的固液相平衡关系,测定了该四元体系在288K时平衡液相的溶解度和密度。依据实验测定的平衡溶解度数据及对应的平衡固相,绘制了该四元体系的平衡相图及密度组成图。研究结果表明：交互四元体系Li+, Mg2+//SO2-4, B4O2-7- H2O 288K时平衡相图中有2个共饱点,5条单变量曲线,4个结晶区对应的平衡固相分别为Li2B4O7·3H2O,Li2SO4·H2O,MgB4O7·9H2O和MgSO4·7H2O。 相似文献
9.
采用等温溶解平衡法开展了三元体系K+,Mg2+∥B4O72--H2O 348K的稳定相平衡研究,获得溶解度数据及平衡液相的密度,折光率,pH值。根据溶解度数据绘制了三元体系稳定相图。该三元体系在348K时的稳定相图含有一个共饱点E、两条单变量曲线AE,BE和两个结晶相区MgB4O7.9H2O(AECA)和K2B4O7·4H2O(BEDB)。共饱点的平衡固相组成为MgB4O7·9H2O和K2B4O7·4H2O,对应的平衡液相组成为w(K2B4O7)=42.28%、w(MgB4O7)=8.11%。研究结果表明,该三元体系属于简单共饱和型,无复盐和固溶体形成。K2B4O7·4H2O和MgB4O7·9H2O互相存在盐溶作用,使得这两种盐的溶解度明显增大。平衡液相的密度、折光率均随溶液中K2B4O7质量分数的增大而增大。 相似文献
10.
1974年在一水晶矿石英脉晶洞中,发现了一种含Ba、Li的硅酸盐新矿物--纤钡锂石。我们对纤钡锂石进行了光性研究、比重测定、差热及热失重分析、红外光谱分析、X射线单晶结构分析等工作,现分述如下。 相似文献
11.
采用CO碳化SiO2和Al3O4负载的Co(NO3)2的方法制备了SiO2和Al3O4负载的Co2C催化剂,采用N2物理吸附、X射线衍射和H2-程序升温还原技术对催化剂进行了表征,并用于催化费托合成反应中.结果显示,需要较长碳化时间才可合成负载的Co2C催化剂;所制催化剂表现出CO加氢生成高碳醇的催化性能,其原因可能在于催化剂表面存在的金属Co物种使CO解离,表面Co物种有利于CO插入,从而导致醇的生成,但体相Co2C则不具有催化活性. 相似文献
13.
近些年来,人们广泛地利用火山岩的主元素或微量元素的特征对火山岩进行地球化学、成因岩石学和构造岩石学的研究。Mullen(1983)利用玄武岩的 MnO、TiO2和P2O5建立大洋型玄武岩的 MnO×10-TiO2-P2O5×10的构造背景判别图(以下简称MTP图)和圈出了大陆拉斑玄武岩在 MTP 图中的分布范围。他选择了能反映玄武岩形成过程中的重要地球化学特征和成因机制的元素组作为该图的端元组分。 相似文献
14.
氟碳铈钡矿Ba3Ce2(CO3)5F2的晶体结构原先被描述为Cm和P2空间群,经单晶X射线衍射方法重测为C2/m空间群;采用2339个独立反射,151个可变参数,R=0.034,Rw=0.05.经检测,未发现明显违反C心布拉维格子的反射;误差允许范围内位移椭球体与所定空间群相容。结构中的原子排列与化合物Ba3La2(CO3)5F2相似,可被描述为平行于(102)层间有序结构,层与层之间通过碳酸根相联结。 相似文献
15.
16.
E. Yu. Li D. V. Grichuk S. N. Shilobreeva D. A. Chareev 《Moscow University Geology Bulletin》2011,66(6):413-422
A thermodynamic model for gas-rock interactions in the system [basalt-SO2-O2±S2] is suggested. Calculations are performed for a wide range of temperatures (100–850°C) and pressures (1–1000 bars). The high-temperature
part of this model was verified by experimental research, which was carried out at 850, 650 and 450°C. The modeling prediction
of interactions in the system [(alumino)silicates SO2-O2±S2] at relatively low temperatures (100–300°C) gives steady mineral associations that are typical for natural secondary quartzites:
quartz-pyrite-hematite-Al-silicates-metal sulfates (Ca, Mg, Na, K, Al, and Fe). The formation of sulfates stabilizes the level
of SO2 concentration in the gas phase; this level falls with a temperature decrease. 相似文献
17.
G. Iezzi F. Cámara R. Oberti G. Della Ventura G. Pedrazzi J-L Robert 《Physics and Chemistry of Minerals》2004,31(6):375-385
This work reports the synthesis of ferri-clinoholmquistite, nominally Li2(Mg3Fe3+2)Si8O22(OH)2, at varying fO2 conditions. Amphibole compositions were characterized by X-ray (powder and single-crystal) diffraction, microchemical (EMPA) and spectroscopic (FTIR, Mössbauer and Raman) techniques. Under reducing conditions ( NNO+1, where NNO = Nickel–Nickel oxide buffer), the amphibole yield is very high (>90%), but its composition, and in particular the FeO/Fe2O3 ratio, departs significantly from the nominal one. Under oxidizing conditions ( NNO+1.5), the amphibole yield is much lower (<60%, with Li-pyroxene abundant), but its composition is close to the ideal stoichiometry. The exchange vector of relevance for the studied system is M2(Mg,Fe2+) M4(Mg,Fe2+) M2Fe3+–1 M4Li–1, which is still rather unexplored in natural systems. Amphibole crystals of suitable size for structure refinement were obtained only at 800 °C, 0.4 GPa and NNO conditions (sample 152), and have C2/m symmetry. The X-ray powder patterns for all other samples were indexed in the same symmetry; the amphibole closest to ideal composition has a = 9.428(1) Å, b = 17.878(3) Å, c = 5.282(1) Å, = 102.06(2)°, V = 870.8(3) Å3. Mössbauer spectra show that Fe3+ is strongly ordered at M2 in all samples, whereas Fe2+ is disordered over the B and C sites. FTIR analysis shows that the amount of CFe2+ increases for increasingly reducing conditions. FTIR data also provide strong evidence for slight but significant amounts of Li at the A sites. 相似文献
18.
我們在前一篇文章里曾討論了Ca2+-HPO42--F1--H2O体系中氟对磷酸盐矿物形成影响的若干方面。为了使該項模拟試驗工作更符合于表生作用条件,我們在叶連俊教授的指导下,在上述实驗体系中增加了一个組分--HCO31-,进行了Ca2+-HPO42--HCO31-F1--H2O体系的試驗研究。其目的为进一步探索在合有HCO31-組分的体系中氟对磷酸盐矿物形成的影响,以及CO32-能否进入磷灰石晶格和磷酸盐矿物与碳酸盐矿物的沉积分异順序等問題。 相似文献
19.
N. V. Chukanov R. K. Rastsvetaeva S. N. Britvin A. A. Virus D. I. Belakovskiy I. V. Pekov S. M. Aksenov B. Ternes 《Geology of Ore Deposits》2011,53(8):767-774
A new heterophyllosilicate mineral schüllerite was found in the L?hley basalt quarry in the Eifel volcanic region, Germany,
as a member of the late mineral assemblage comprising nepheline, leucite, augite, phlogopite, magnetite, titanite, fresnoite,
barytolamprophyllite, fluorapatite, perovskite, and pyrochlore. Flattened brown crystals of schüllerite up to 0.5 × 1 × 2
mm in size and their aggregates occur in miarolic cavities of alkali basalt. The mineral is brittle, with a Mohs hardness
3–4 and perfect cleavage parallel to (001). D
calc = 3.974 g/cm3. Its IR spectrum is individual and does not contain bands of OH−, CO32− or H2O. Schüllerite is biaxial (−), α = 1.756(3), β = 1.773(4), γ = 1.780(4), 2V
meas = 40(20)°. Dispersion is weak, r < ν. Pleochroism is medium X > Y > Z, brown to dark brown. Chemical composition (electron microprobe, mean of five-point analyses, Fe2+/Fe3+ ratio determined by the X-ray emission spectroscopic data, wt %): 3.55 Na2O, 0.55 K2O, 3.89 MgO, 2.62 CaO, 1.99 ArO, 28.09 BaO, 3.43 FeO, 8.89 Fe2O3, 1.33 Al2O3, 11.17 TiO2, 2.45 Nb2O5, 26.12 SiO2, 2.12 F, −0.89 -O=F2, 98.98 in total. The empirical formula is (Ba1.68Sr0.18K0.11Na1.05Ca0.43Mn0.47Mg0.88Fe0.442+Fe1.023+Ti1.28Nb0.17Al0.24)Σ7.95Si3.98O16.98F1.02. The crystal structure was refined on a single crystal. Schüllerite is triclinic, space group P1, unit cell parameters: a = 5.4027(1), b = 7.066(4), c = 10.2178(1)?, α = 99.816(1), β = 99.624(1), γ = 90.084(1)°, V = 378.75(2) ?3, Z = 1. The strongest lines of the X-ray powder diffraction pattern [d, ?, (I, %)]: 9.96(29), 3.308(45), 3.203(29), 2.867(29), 2.791(100), 2.664(46), 2.609(36), 2.144(52). The mineral was named in honor
of Willi Schüller (born 1953), an enthusiastic, prominent amateur mineral collector, and a specialist in the mineralogy of
Eifel. Type specimens have been deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow,
registration no. 3995/1,2. 相似文献
20.
An olivine grain from a peridotite nodule 9206 (Udachnaya kimberlite, Siberia) was investigated by TEM methods including
AEM, HRTEM, SAED and EELS techniques. A previous study of the 9206 olivine sample revealed OH absorption bands in the IR spectrum
and abundant nanometer-sized OH-bearing inclusions, of hexagonal-like or lamellar shape. Inclusions, which are several hundred
nm in size, consist of 10 ? phase, talc and serpentine (chrysotile and lizardite). The lamellar (LI) and hexagon-like small
inclusions of several ten nm in size (SI) are the topic of the present paper. AEM investigations of the inclusions reveal
Mg, Fe and Si as cations only. The Mg/Si and Fe/Si atomic ratios are lower in the inclusions than in the host olivine. The
Si concentration in the olivine host and both lamellar inclusions and small inclusions is the same. A pre-peak at 528eV was
observed in EEL spectra of LI and SI, which is attributed to OH− or Fe3+. From these data it is concluded that there is a OH−- or Fe3+-bearing cation-deficient olivine-like phase present.
HRTEM lattice fringe images of LI and SI exhibit modulated band-like contrasts, which are superimposed onto the olivine lattice.
Diffraction patterns (Fourier-transforms) of the HREM images as well as SAED patterns show that the band-like contrasts in
HRTEM images of the inclusions are caused by periodic modulations of the olivine lattice. Three kinds of superperiodicity
in the olivine structure such as 2a, 3a and 3c, were observed in SAED patterns. The corresponding olivine supercells labelled
here as Hy-2a, Hy-3a and Hy-3c were derived. The M1-vacancies located in the (100) and (001) octahedral layers of the olivine
lattice are suggested to form ordered arrays of planar defects (PD), which cause the band-like contrasts in HRTEM patterns
as well as the superperiodicity in the SAED patterns.
The vacancy concentrations as well as the chemical composition of Hy-2a, Hy-3a and Hy-3c olivine supercells were calculated
using crystal chemical approaches, assuming either {(OH)<
O−V"
Me−(OH)<
O}↔, or {F
e
<
Fe
−H
Me
′}↔ or {2F
e
<
Fe
−V
Me
"}↔ point defect associates. The calculated theoretical compositions Mg1.615Fe+2
0.135v0.25SiO4H0.5 (Hy-2a) and Mg1.54Fe2+
0.12v0.33SiO4H0.66 (Hy-3a and Hy-3c) are in a good agreement with the AEM data on inclusions. Hy-2a, Hy-3a and Hy-3c are considered to be a
hydrous olivine with the extended chemical formula (Mg1-yFe2+
y)2−xvxSiO4H2x. The crystal structure of hydrous olivine is proposed to be a modular olivine structure with Mg-vacant modules. The crystal
chemical formula of hydrous olivines in terms of a modular structure can be written as [MgSiO4H2] · 3[Mg1.82Fe0.18SiO4] for Hy-2a, [MgSiO4H2] · 2[Mg1.82Fe0.18SiO4] for Hy-3a and Hy-3c.
Hydrous olivine is suggested to be exsolved from the olivine 9206, which has been initially saturated by OH-bearing point
defects. The olivine 9206 hydration as well as the following exsolution of hydrous olivine inclusions is suggested to occur
at high pressure-high temperature conditions of the upper mantle.
Received: 15 January 2001 / Accepted: 2 July 2001 相似文献