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1.
A new mineral fivegite has been identified in a high-potassium hyperalkaline pegmatite at Mt. Rasvumchorr in the Khibiny alkaline complex of the Kola Peninsula in Russia. This mineral is a product of the hydrothermal alteration of delhayelite (homoaxial pseudomorphs after its crystals up to 2 × 3 × 10 cm in size). Hydrodelhayelite, pectolite, and kalborsite are products of fivegite alteration. The associated minerals are aegirine, potassic feldspar, nepheline, sodalite, magnesiumastrophyllite, lamprophyllite, lomonosovite, shcherbakovite, natisite, lovozerite, tisinalite, ershovite, megacyclite, shlykovite, cryptophyllite, etc. Areas of pure unaltered fivegite are up to 2 mm in width. The mineral is transparent and colorless; its luster is vitreous to pearly. Its Cleavage is perfect (100) and distinct (010). Its Mohs hardness is 4, D(meas) = 2.42(2), and D(calc) = 2.449 g/cm3. Fivegite is optically biaxial positive: α 1.540(1), β 1.542(2), γ 1.544(2), and 2V(meas) 60(10)°. Its orientation is X = a, y = c, and Z = b. Its IR spectrum is given. Its chemical composition (wt %; electron microprobe, H2O determined by selective sorption) is as follows: 1.44 Na2O, 19.56 K2O, 14.01 CaO, 0.13 SrO, 0.03 MnO, 0.14 Fe2O3, 6.12 Al2O3, 50.68 SiO2, 0.15 SO3, 0.14 F, 3.52 Cl, 4.59 H2O; −O = −0.85(Cl,F)2; total 99.66. The empirical formula based on (Si + Al + Fe) = 8 is H4.22K3.44Na0.39Ca2.07Sr0.01Fe0.01Al1.00Si6.99O21.15F0.06Cl0.82(SO4)0.02. The simplified formula is K4Ca2[AlSi7O17(O2 − x OH x ][(H2O)2 − x OH x ]Cl (X = 0−2). Fivegite is orthorhombic: Pm21 n, a = 24.335(2), b = 7.0375(5), c = 6.5400(6) ?, V = 1120.0(2) ?3, and Z = 2. The strongest reflections of the X-ray powder pattern are as follows (d, ?, (I, %), [hkl]): 3.517(38) [020], 3.239(28) [102], 3.072(100) [121, 701], 3.040(46) [420, 800, 302], 2.943 (47) [112], 2.983(53) [121], 2.880 (24) [212, 402], 1.759(30) [040, 12.2.0]. The crystal structure was studied using a single crystal: R hkl = 0.0585. The base of fivegite structure is delhayelite-like two-layer terahedral blocks [(Al,Si)4Si12O34(O4 − x OH x )] linked by Ca octahedral chains. K+ and Cl− are localized in zeolite-like channels within the terahedral blocks, whereas H2O and OH occur between the blocks. The mineral is named in memory of the Russian geological and mining engineer Mikhail Pavlovich Fiveg (1899–1986), the pioneering explorer of the Khibiny apatite deposits. The type specimen is deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences in Moscow. The series of transformations is discussed: delhayelite K4Na2Ca2[AlSi7O19]F2Cl—fivegite K4Ca2[AlSi7O17(O2 − x OH x ]Cl—hydrodelhayelite KCa2[AlSi7O17(OH)2](H2O)6 − x .  相似文献   

2.
The structural variations along the solid solution Sr2−x Ba x MgSi2O7 (0 ≤ x ≤ 2), combined to the high-pressure characterization of the two end-members, have been studied. A topological change from the tetragonal (melilite-type) to the monoclinic (melilite-related) structure along the join Sr2MgSi2O7 (e.g., P[`4]21 m P\bar{4}2_{1} m )–Ba2MgSi2O7 (e.g., C2/c) occurs with a Ba content higher than 1.6 apfu. Favored in the crystallization from a melt, the tetragonal form has a tetrahedral sheet topology exclusively based on five-membered rings, which provide a regular “4 up + 4 down” ligand arrangement. In contrast, the melilite-related structure, favored by solid-state reaction synthesis, is made by alternating six- and four-membered tetrahedral rings, which give an asymmetric arrangement of alternated “5 up + 3 down” and “3 up + 5 down” ligands around Sr or Ba. This latter configuration is characterized by an additional degree of freedom with Ba polyhedra hosted in the interlayer with a more irregular and compact coordination and longer Ba–O bond distances. Further insights into the relationships between the two melilite typologies were achieved by investigating the in situ high-pressure behavior of these systems. The synchrotron high-pressure experiments allowed to calculate the elastic moduli for the Sr melilite-type end-member and for the Ba monoclinic polymorph (Sr2MgSi2O7: K T0 = 107, K a=b  = 121, and K c  = 84 GPa; m-Ba2MgSi2O7: K T0 = 85, K a  = 96, K b  = 72, and K c  = 117 GPa) and compare them with those reported in the literature for ?kermanite (Ca2MgSi2O7). The results show that, although the volume of Ba polyhedron in tetragonal polymorphs is larger than in the monoclinic forms, the interlayer compressibility is significantly lower in the former structures due to the occurrence of very short Ba–O distances. This unfavored Ba environment also makes tetragonal Ba2MgSi2O7 a metastable phase at room conditions, possibly favored by high pressure. However, no phase transition occurs from monoclinic to tetragonal form due to kinetic hindrance in reconstructing the sheet topology.  相似文献   

3.
The 10?-phase, Mg3Si4O10(OH)2 · nH2O, where n = 0.65÷2, belongs to the group of dense hydrous magnesium silicates (DHMS), which were produced in experiments and are regarded as hypothetical mineral carriers for H2O in the mantle. However, DHMS were almost never observed in nature. The only exception is the finding of the 10?-phase as nanoinclusions in olivines from mantle nodules in kimberlites. The inclusions with sizes of a few ten nanometers have a pseudohexagonal habit and are characterized by the presence of voids free of solids. The 10?-phase fills the equatorial parts of the inclusions, and, in the majority of inclusions, it is replaced by the low-pressure serpentine + talc assemblage. Based on the analysis of electron microscope images, a model was proposed for the solid-state formation of inclusions, the precursory material of which was transformed to the 10?-phase with the liberation of a water fluid. According to this model, the formation of hydrous nanoinclusions and their subsequent autoserpentinization occurred without the influx of H2O from the external medium through the mobilization of intrinsic hydroxyl-bearing point defects trapped during olivine crystallization. The subsequent autoserpentinization of the inclusions occurred during decompression owing to interaction between the inclusion material and the host olivine matrix. The process was accompanied by the partial exhaustion of the fluid phase and the replacement 10?-phase + H2O = Serp + Tc. The criterion for the credibility of the model is the conservation of the volume of material during the reaction at P = const and T = const. Original Russian Text ? N.R. Khisina, R. Wirth, 2008, published in Geokhimiya, 2008, No. 4, pp. 355–363.  相似文献   

4.
The thermoelastic parameters of synthetic Ca3Al2Si3O12 grossular garnet were examined in situ at high-pressure and high-temperature by energy dispersive X-ray diffraction, using a Kawai-type multi-anvil press apparatus coupled with synchrotron radiation. Measurements have been conducted at pressures up to 20 GPa and temperatures up to 1,650 K: this P, T range covered the entire high-P, T stability field of grossular garnet. The analysis of room temperature data yielded V 0,300 = 1,664 ± 2 ?3 and K 0 = 166 ± 3 GPa for K￠0 K^{\prime}_{0} fixed to 4.0. Fitting of our P–V–T data by means of the high-temperature third order Birch–Murnaghan or the Mie–Grüneisen–Debye thermal equations of state, gives the thermoelastic parameters: (∂K 0,T /∂T) P  = −0.019 ± 0.001 GPa K−1 and α 0,T  = 2.62 ± 0.23 × 10−5 K−1, or γ 0 = 1.21 for fixed values q 0 = 1.0 and θ 0 = 823 (Isaak et al. Phys Chem Min19:106–120, 1992). From the comparison of fits from two different approaches, we propose to constrain the bulk modulus of grossular garnet and its pressure derivative to K T0 = 166 GPa and K￠T0 K^{\prime}_{T0}  = 4.03–4.35. Present results are compared with previously determined thermoelastic properties of grossular-rich garnets.  相似文献   

5.
Using a conventional high-T furnace, the solid solutions between magnesiochromite and manganochromite, (Mg1−x Mn x )Cr2O4 with x = 0.00, 0.19, 0.44, 0.61, 0.77 and 1.00, were synthesized at 1,473 K for 48 h in open air. The ambient powder X-ray diffraction data suggest that the V–x relationship of the spinels does not show significant deviation from the Vegard’s law. In situ high-T powder X-ray diffraction measurements were taken up to 1,273 K at ambient pressure. For the investigated temperature range, the unit-cell parameters of the spinels increase smoothly with temperature increment, indicating no sign of cation redistribution between the tetrahedral and octahedral sites. The V–T data were fitted with a polynomial expression for the volumetric thermal expansion coefficient (aT = a0 + a1 T + a2 T - 2 \alpha_{T} = a_{0} + a_{1} T + a_{2} T^{ - 2} ), which yielded insignificant a 2 values. The effect of the composition on a 0 is adequately described by the equation a 0 = [17.7(8) − 2.4(1) × x] 10−6 K−1, whereas that on a 1 by the equation a 1 = [8.6(9) + 2.1(11) × x] 10−9 K−2.  相似文献   

6.
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   

7.
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   

8.
The structural evolution with pressure and the equations of state of three members of the brownmillerite solid solution, Ca2(Fe2−x Al x )O5, have been determined by single-crystal X-ray diffraction up to a maximum pressure of 9.73 GPa. The compositions of the samples were x = 0.00 and x = 0.37 (with Pnma symmetry) and x = 0.55 (with I2mb symmetry). No phase transitions were observed in the experiments. The equation of state parameters determined from the pressure-volume data are K 0T = 128.0 (7) GPa, K′0 = 5.8 (3) for the sample with x = 0.00, K 0T = 131 (2) GPa, K′0 = 5.5 (4) for x = 0.37, and K 0T = 137.5 (6) GPa, K′0 = 4 for x = 0.55. The bulk modulus therefore increases with Al content, being 11% higher in the x = 0.55 sample than in the Al-free sample. The unit-cell compression is anisotropic, with the c-axis being stiffer than a or b, and the anisotropy increases with increasing Al content of the structure. The structural response to pressure of all samples is similar. The (Al,Fe)O4 tetrahedra and the (Al,Fe)O6 octahedra undergo approximately isotropic compression. There is an increase in the twists of the chains of corner-sharing (Al,Fe)O4 tetrahedra, and an increase in the tilts of the (Al,Fe)O6 octahedra, because these framework polyhedra are stiffer than the Ca–O bonds to the extra-framework Ca site. The alignment of the two shortest Ca–O bonds sub-parallel to [001] accounts for the relative stiffness of the c-axis and thus the elastic anisotropy. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

9.
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   

10.
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11.
A natural Ca-poor pigeonite (Wo6En76Fs18) from the ureilite meteorite sample PCA82506-3, free of exsolved augite, was studied by in situ high-temperature single-crystal X-ray diffraction. The sample, monoclinic P21/c, was annealed up to 1,093°C to induce a phase transition from P21/c to C2/c symmetry. The variation with increasing temperature of the lattice parameters and of the intensity of the b-type reflections (h + k = 2n + 1, present only in the P21/c phase) showed a displacive phase transition P21/c to C2/c at a transition temperature T Tr = 944°C, first order in character. The Fe–Mg exchange kinetics was studied by ex situ single-crystal X-ray diffraction in a range of temperatures between the closure temperature of the Fe–Mg exchange reaction and the transition temperature. Isothermal disordering annealing experiments, using the IW buffer, were performed on three crystals at 790, 840 and 865°C. Linear regression of ln k D versus 1/T yielded the following equation: ln k\textD = - 3717( ±416)/T(K) + 1.290( ±0.378);    (R2 = 0.988) \ln \,k_{\text{D}} = - 3717( \pm 416)/T(K) + 1.290( \pm 0.378);\quad (R^{2} = 0.988) . The closure temperature (T c) calculated using this equation was ∼740(±30)°C. Analysis of the kinetic data carried out taking into account the e.s.d.'s of the atomic fractions used to define the Fe–Mg degree of order, performed according to Mueller’s model, allowed us to retrieve the disordering rate constants C 0 K dis+ for all three temperatures yielding the following Arrhenius relation: ln( C0 K\textdis + ) = ln K0 - Q/(RT) = 20.99( ±3.74) - 26406( ±4165)/T(K);    (R2 = 0.988) \ln \left( {C_{0} K_{\text{dis}}^{ + } } \right) = \ln \,K_{0} - Q/(RT) = 20.99( \pm 3.74) - 26406( \pm 4165)/T(K);\quad (R^{2} = 0.988) . An activation energy of 52.5(±4) kcal/mol for the Fe–Mg exchange process was obtained. The above relation was used to calculate the following Arrhenius relation modified as a function of X Fe (in the range of X Fe = 0.20–0.50): ln( C0 K\textdis + ) = (21.185 - 1.47X\textFe ) - \frac(27267 - 4170X\textFe )T(K) \ln \left( {C_{0} K_{\text{dis}}^{ + } } \right) = (21.185 - 1.47X_{\text{Fe}} ) - {\frac{{(27267 - 4170X_{\text{Fe}} )}}{T(K)}} . The cooling time constant, η = 6 × 10−1 K−1 year−1 calculated on the PCA82506-3 sample, provided a cooling rate of the order of 1°C/min consistent with the extremely fast late cooling history of the ureilite parent body after impact excavation.  相似文献   

12.
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   

13.
Any progress in our understanding of low-temperature mineral assemblages and of quantitative physico-chemical modeling of stability conditions of mineral phases, especially those containing toxic elements like selenium, strongly depends on the knowledge of structural and thermodynamic properties of coexisting mineral phases. Interrelation of crystal chemistry/structure and thermodynamic properties of selenium-containing minerals is not systematically studied so far and thus any essential generalization might be difficult, inaccurate or even impossible and erroneous. Disagreement even exists regarding the crystal chemistry of some natural and synthetic selenium-containing phases. Hence, a systematic study was performed by synthesizing ferric selenite hydrates and subsequent thermal analysis to examine the thermal stability of synthetic analogues of the natural hydrous ferric selenite mandarinoite and its dehydration and dissociation to unravel controversial issues regarding the crystal chemistry. Dehydration of synthesized analogues of mandarinoite starts at 56–87?°C and ends at 226–237?°C. The dehydration happens in two stages and two possible schemes of dehydration exist: (a) mandarinoite loses three molecules of water in the first stage of the dehydration (up to 180?°C) and the remaining two molecules of water will be lost in the second stage (>180?°C) or (b) four molecules of water will be lost in the first stage up to 180?°C and the last molecule of water will be lost at a temperature above 180?°C. Based on XRD measurements and thermal analyses we were able to deduce Fe2(SeO3)3·(6-x)H2O (x?=?0.0–1.0) as formula of the hydrous ferric selenite mandarinoite. The total amount of water apparently affects the crystallinity, and possibly the stability of crystals: the less the x value, the higher crystallinity could be expected.  相似文献   

14.
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   

15.
根据X射线衍射(XRD)分析发现: A Fe3(SO4)2(OH)6(A=K+、H3O+)系列铁钒的XRD数据十分相近,难以用XRD区别,需通过能谱(EDS)辅助分析,才能区分此类铁矾。另外,此类铁矾的003和107面网间距d随K+含量增大而增大,且呈一元三次方程的关系;而033和220面网间距d随K+含量增大而减小,呈一元二次方程的关系。对该现象从铁矾晶体结构方面进行解释:K+、H3O+离子位于较大空隙中,且沿着Z轴方向排列,当K+、H3O+离子之间相互替换时,会导致该铁矾晶体结构在Z轴方向有较明显的变化。  相似文献   

16.
纤钡锂石产于湖南临武香花岭地区一水晶矿锂云母石英脉晶洞中,与锂云母、石英等矿物共生。矿物为浅黄白色,丝绢光泽,呈针状、纤维状、放射状或平行束状集合体,纤维长达1厘米。经X射线单晶及粉晶衍射测定:该矿物属斜方晶系,空间群Ccca,晶胞参数:a=13.60(?),b=20.24(?),e=5.16(?)。最强衍射线为:10.12(?)(100) 4.05(?)(78) 3.39(?)(91) 2.605(?)(31)2.390(?)(28)。  相似文献   

17.
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   

18.
《岩石矿物学杂志》2000,19(4):376-381
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19.
柴达木盆地跃进地区E31、N1、N21碎屑岩储层特征   总被引：5，自引：0，他引：5  
通过 15口井近百个铸体片的鉴定及压汞数据的分析,对跃进地区E31、N1、N21碎屑岩储层取得如下认识 :①长石砂岩、岩屑长石砂岩、长石岩屑砂岩为主,成分成熟度和结构成熟度均较低;②储层经历压实压溶作用、成岩自生矿物胶结和溶解作用,剩余原生粒间孔占绝对优势,相同层位地层在跃东和跃西因埋藏深度不同导致成岩-孔隙演化史也不同,西区储层物性明显优于东区;③储层主要发育于水上分流河道、砂坪和辫状河道微相,碎屑的成份和结构成熟度、填隙物含量、成岩环境对储层性质有重要影响;④西区E31储层属高孔中渗的Ⅱ类储层,大孔细喉道组合特征,储集物性较佳,东区E31储层属特低孔特低渗的Ⅴ类储层,中孔微细喉道组合特征,储层物性不理想,N1储层属低孔特低渗的Ⅳ-Ⅴ类储层,大孔小喉道组合特征,渗透率不佳.  相似文献   

20.
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   

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