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1.
The dielectric constants and dissipation factors of topaz, scapolite and orthoclase were determined at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: topaz κ′ a =6.61 tan δ=0.0005 κ′ b =6.82 tan δ=0.0007 κ′ c =6.81 tan δ=0.0007 orthoclase κ′ a =4.69 tan δ=0.0007 κ′ b =5.79 tan δ=0.0007 κ′ c =5.63 tan δ=0.0011 κ′ 11 =4.72 κ′ 22 =5.79 κ′ 33 =5.76 scapolite κ′ a =6.74 tan δ=0.0004 κ′ c =8.51 tan δ=0.0004 The deviation (Δ) between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of ion polarizabilities according to α D (mineral)=∑αD (ions) for topaz is 2.5%. The large deviations of orthoclase and scapolite from the oxide additivity rule with δ=+7.2 and + 17.6%, respectively, are attributed to “rattling” K ions in orthoclase and “rattling” (Na,K,Ca) ions and disordered O= and Cl- ions in scapolite.  相似文献   

2.
The dielectric constants and dissipation factors of synthetic tephroite (Mn2SiO4), fayalite (Fe3SiO4) and a forsteritic olivine (Mg1.80Fe0.22SiO4) were measured at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: tephroite, κ′a= 8.79 tan δa = 0.0006 κ′b = 10.20 tan δb = 0.0006 κ′c= 8.94 tan δc= 0.0008 fayalite, gk′a = 8.80 tan δa = 0.0004 gk′b= 8.92 tan δb = 0.0018 gk′c = 8.58 tan δc = 0.0010 olivine, gk′a = 7.16 tan δa = 0.0006 gk′b = 7.61 tan δb = 0.0008 gk′c = 7.03 tan δc = 0.0006 The low dielectric constant and loss of the fayalite indicate an exceptionally low Fe3+ content. An FeO polarizability of 4.18 Å3, determined from αD(FeO) = [αD (Fe2SiO4)-αD(SiO2)]/2, is probably a more reliable value for stoichiometric FeO than could be obtained from FexO where x = 0.90–0.95. The agreement between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to αD(M2M′X2) = 2αD(MX) + αD(M′X2) is ～+2.8% for tephroite and +0.2% for olivine. The deviation from additivity in tephroite is discussed.  相似文献   

3.
The dielectric constants and dissipation factors of LiAlSi2O6, CaAl2Si2O8 and CaMgSi2O6 in both the crystalline (α-spodumene, anorthite, and diopside) and amorphous forms were determined at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: spodumene κ′ 11=7.30 tan δ= 0.0007 κ′22=8.463 tan δ= 0.0002 κ′33 =11.12 tan δ= 0.0007 anorthite κ′ a *=5.47 tan δ= 0.0009 κ′b *=8.76 tan δ= 0.0010 κ′c *=7.19 tan δ= 0.0013 diopside κ′11=9.69 tan δ= 0.0016 κ′22 = 7.31 tan δ= 0.0007 κ′33=7.29 tan δ= 0.00019 LiAlSi2O6 κ′=8.07 tan δ= 0.047 amorphous CaAl2Si2O8 κ′=7.50 tan δ= 0.0024 amorphous CaMgSi2O6 κ′=8.89 tan δ= 0.0021 amorphous The dielectric properties of a spodumene glass, progressively crystallized at different conditions, were also determined. As the crystallization temperature was increased from 720 to 920° C, κ′ increased from 6.22 to 6.44. The dissipation factor, tan δ, remained constant at 0.020. Similarly, as the crystallization time at 750° C increased from 0.5 hr to 6.0 hr, κ′ increased from 6.28 to 6.35. The deviations of the measured dielectric polarizabilities as determined from the Clausius-Mosotti equation from those calculated from the sum of oxide polarizabilities according to α D(mineral, glass) = σ α D(oxides) are +7.4% for α-spodumene, +1.2% for diopside, and +28.0, +19.6 and +15.9% for amorphous spodumene, anorthitie and diopside compositions, respectively. Positive deviations in α-spodumene and anorthite are consistent with lower than normal apparent cation bond valence sums and are believed to be evidence for loosely bonded “rattling” Li and Ca ions. Diopside, with Ca and Mg ions having normal bond valence sums, exhibits no abnormal deviation from additivity. Larger positive deviations in amorphous SiO2, LiAlSi2O6, CaAl2Si2O8 and CaMgSi2O6 are postulated to arise from a combination of loosely bonded cations and disordered O= ions where the oxygen dielectric polarizability increased from its normal value of 2.0 Å3 in well-behaved oxides to 2.2–3.0 Å3 in the amorphous phases.  相似文献   

4.
Using fused SiO2, CaF2, and SrF2 samples with accurately known dielectric constants, we have evaluated the accuracy and precision of two-terminal dielectric constant measurements on small single crystals using empirically determined edge corrections. Values of κ′ at 1 MHz of 3.836±0.05 for silica, 6.814±0.07 for CaF2 and 6.463±0.09 for SrF2 indicate an accuracy and precision of 1.0–1.5% for samples having areas of 0.05–1.0 cm2. Dielectric constants of BeO, MgO, and CaO measured by this technique are: BeO, κ′a=6.87 and κ′c=7.74; MgO, κ′= 9.90; and CaO, κ′=11.95 where κ′a and κ′c are the dielectric constants parallel to the a and c axes, respectively. Dielectric loss measurements on CaO in vacuum between 5–400 K at 10–105 Hz indicate significant dispersion at temperatures higher than 300 K, but the effect of the losses on the dielectric constant is less than 1% at 1 MHz and 300 K.  相似文献   

5.
The dielectric constants and dielectric loss values of BeAl2O4 (chrysoberyl), MgAl2O4 (spinel), Be2SiO4 (phenacite), and Mg2SiO4 (forsterite) were measured at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: chrysoberyl, κ′ a =9.436, κ′ b =9.071, κ′ c =8.269; spinel, κ′ a =8.18; phenacite, κ′ a =6.28, κ′ c =6.06; and forsterite, κ′ a =6.867, κ′ b =7.392, κ′ c =6.739. The agreement between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to αD(M2M′X4) = 2αD(MX)+αD(M′X2) is ~ 1.0%.  相似文献   

6.
The comparative compressibility and high-pressure stability of a natural epidote (0.79 Fe-total per formula unit, Fetot pfu) and clinozoisite (0.40 Fetot pfu) were investigated by single-crystal X-ray diffraction and Raman spectroscopy. The lattice parameters of both phases exhibit continuous compression behavior up to 30 GPa without evidence of phase transformation. Pressure–volume data for both phases were fitted to a third-order Birch–Murnaghan equation of state with V 0 = 461.1(1) Å3, K 0 = 115(2) GPa, and \(K_{0}^{'}\) = 3.7(2) for epidote and V 0 = 457.8(1) Å3, K 0 = 142(3) GPa, and \(K_{0}^{'}\) = 5.2(4) for clinozoisite. In both epidote and clinozoisite, the b-axis is the stiffest direction, and the ratios of axial compressibility are 1.19:1.00:1.15 for epidote and 1.82:1.00:1.19 for clinozoisite. Whereas the compressibility of the a-axis is nearly the same for both phases, the b- and c-axes of the epidote are about 1.5 times more compressible than in clinozoisite, consistent with epidote having a lower bulk modulus. Raman spectra collected up to 40.4 GPa also show no indication of phase transformation and were used to obtain mode Grüneisen parameters (γ i) for Si–O vibrations, which were found to be 0.5–0.8, typical for hydrous silicate minerals. The average pressure coefficient of Raman frequency shifts for M–O modes in epidote, 2.61(6) cm?1/GPa, is larger than found for clinozoisite, 2.40(6) cm?1/GPa, mainly due to the different compressibility of FeO6 and AlO6 octahedra in M3 sites. Epidote and clinozoisite contain about 2 wt% H2O are thus potentially important carriers of water in subducted slabs.  相似文献   

7.
Calcic amphiboles coexisting with epidotegroup minerals (zoisite, clinozoisite, epidote) and/or clinopyroxene±plagioclase±quartz±garnet occur in amphibolites and calc-silicate rocks that underwent amphibolite to lower granulite-facies metamorphism in the Acadian metamorphic high of central Massachusetts, USA. Across the region, peak metamorphic conditions range from about 580° C and 6.2 kbar to 730° C and 6.3 kbar. The coexistence of most Ca-amphiboles with Fe3+-rich epidote-group minerals suggests the presence of Fe3+ in most of these amphiboles. An empirical Fe3+ estimation for the microprobe analyses is based on two constraints: the Na?Ca content of the M4 sites of Ca-saturated, gravimetrically analyzed hornblendes gives the relation: Ca(M4) c =-1.479 Na(M4) c +2 (c=corrected). The second constraint is the stoichiometric equation Ca(M4)+Na(M4)+FM=15, where FM is the sum of all cations exclusive of Ca, Na, and K. Solving the two equations simultaneously gives: 20.185=0.479 Ca(M4)+1.479 ΣFM. Starting with the uncorrected values of Ca(M4) u and ΣFM(M4) u (u = uncorrected) of the all ferrous formula, the normalization factor NF for calculating the corrected cations of the ferric formulas is: 20.185/(0.478 Ca(M4) u +1.479 ΣFM u ). From the deficient oxygen the Fe3+ content which is equal to 2(23-ΣOX) can be calculated. Determinations of Fe3+ contents of four hornblende separates by Mössbauer spectroscopy are in agreement with the calculated values. The Ca-amphiboles show systematic changes in composition with increasing grade of metamorphism within the amphibolite and lower granulite-facies zones: increasing edenite and tschermakite substitution, increasing Ti content, and increasing Fe2+/(Fe2++Mg) ratio. In addition, the coexisting clinopyroxenes are also characterized by an increase in Fe2+/(Fe2++Mg) ratio. In quartz-free rocks with coexisting Ca-amphibole and plagioclase there is an increase in the ratio X Ab/X Ed, where X Ab=Na/(Na+Ca) in plagioclase and X Ed=Na in the amphibole A-site. These chemical changes in mineral composition together with the disappearance of epidote at the transition to granulite-facies metamorphic conditions are attributed to the continuous reaction: albite+epidote+Fe-Mg hornblende→Fe?Mg clinopyroxene+anorthite+(NaAlSi-1)Hbl+H2O.  相似文献   

8.
The behavior of a natural topaz, Al2.00Si1.05O4.00(OH0.26F1.75), has been investigated by means of in situ single-crystal synchrotron X-ray diffraction up to 45 GPa. No phase transition or change in the compressional regime has been observed within the pressure-range investigated. The compressional behavior was described with a third-order Birch–Murnaghan equation of state (III-BM-EoS). The III-BM-EoS parameters, simultaneously refined using the data weighted by the uncertainties in P and V, are as follows: K V = 158(4) GPa and K V ′ = 3.3(3). The confidence ellipse at 68.3 % (Δχ2 = 2.30, 1σ) was calculated starting from the variance–covariance matrix of K V and K′ obtained from the III-BM-EoS least-square procedure. The ellipse is elongated with a negative slope, indicating a negative correlation of the parameters K V and K V ′, with K V = 158 ± 6 GPa and K V ′ = 3.3 ± 4. A linearized III-BM-EoS was used to obtain the axial-EoS parameters (at room-P), yielding: K(a) = 146(5) GPa [β a = 1/(3K(a)) = 0.00228(6) GPa?1] and K′(a) = 4.6(3) for the a-axis; K(b) = 220(4) GPa [β b = 0.00152(4) GPa?1] and K′(b) = 2.6(3) for the b-axis; K(c) = 132(4) GPa [β c = 0.00252(7) GPa?1] and K′(c) = 3.3(3) for the c-axis. The elastic anisotropy of topaz at room-P can be expressed as: K(a):K(b):K(c) = 1.10:1.67:1.00 (β a:β b:β c = 1.50:1.00:1.66). A series of structure refinements have been performed based on the intensity data collected at high pressure, showing that the P-induced structure evolution at the atomic scale is mainly represented by polyhedral compression along with inter-polyhedral tilting. A comparative analysis of the elastic behavior and P/T-stability of topaz polymorphs and “phase egg” (i.e., AlSiO3OH) is carried out.  相似文献   

9.
The Grüneisen ratio, γ, is defined as γy=αK TV/Cv. The volume dependence of γ(V) is solved for a wide range in temperature. The volume dependence of αK T is solved from the identity (? ln(αK T)/? ln V)T ≡ δ T-K′. α is the thermal expansivity; K T is the bulk modulus; C V is specific heat; and δ Tand K′ are dimensionless thermoelastic constants. The approach is to find values of δ T and K′, each as functions of T and V. We also solve for q=(? ln γ/? ln V) where q=δ T -K′+ 1-(? ln C V/? ln V)T. Calculations are taken down to a compression of 0.6, thus covering all possible values pertaining to the earth's mantle, q=? ln γ/? ln V; δ T=? ln α/? ln V; and K′= (?K T/?P)T. New experimental information related to the volume dependence of δ T, q, K′ and C V was used. For MgO, as the compression, η=V/V 0, drops from 1.0 to 0.7 at 2000 K, the results show that q drops from 1.2 to about 0.8; δ T drops from 5.0 to 3.2; δ T becomes slightly less than K′; ? ln C V/? In V→0; and γ drops from 1.5 to about 1. These observations are all in accord with recent laboratory data, seismic observations, and theoretical results.  相似文献   

10.
The main purpose of this study is to model the δ13C values of methane derived from coal by combining kinetic-simulating experiment with the gas chromatography-isotope ratio mass spectrum (GC-IRMS) analysis. The stable carbon isotopic variation of methane in pyrolysates with heating temperature indicates that the assumptions for both a constant kinetic isotope effect (α) and a uniform initial isotopic composition (δ13Co) are impractical for explaining the carbon isotopic fractionation during coalification. For purposes of simplification, two approaches are used in this paper to deal with the heterogeneity of terrestrial organic matter. One is that, assuming a uniform initial isotopic composition (i.e., δ13Ci, o=δ13Co) for all methane-generating precursors in coal, the isotopic variation of methane is fitted by adjusting ΔEa, i (Ea13C, i−Ea12C, i) for each hypothetical reaction. The other is that, assuming a constant kinetic isotope effect during the whole gas formation, that is all ΔEa, i values are identical, the modeling of methane isotopic composition is achieved by changing the 13CH4 generation potential of each reaction (fi, 13C), namely, by adjusting the initial δ13C value (δ13Ci, o) for each methane-generating precursor. Results of the kinetic calculation shows that the two simulating methods can yield a similar result at a geological heating rate of 2 °C/My, which further demonstrates that those natural gases with methane δ13C value being approximately −36‰ are possibly sourced from the upper Triassic coal measure strata in the Northwestern Sichuan Basin.  相似文献   

11.
Using single-crystal X-ray diffraction from a diamond anvil cell, the compressibility of a synthetic fluorapatite was determined up to about 7?GPa. The compression pattern was anisotropic, with greater change along a than c. Unit cell parameters varied linearly with β a =3.32(8)?10?3 and β c =2.40(5)?10?3 GPa?1, giving a ratio β a :β c =1.38:1. Data fitted with a third-order Birch-Murnaghan EOS yielded a bulk modulus of K 0=93(4)?GPa with K′=5.8(1.8). The evolution of the crystal structure of fluorapatite was analysed using data collected at room pressure, at 3.04 and 4.72?GPa. The bulk modulus of phosphate tetrahedron is about three times greater than the bulk modulus of calcium polyhedra. The values were 270(10), 100(4) and 86(3) GPa for P, Ca1 (nine-coordinated) and Ca2 (seven-coordinated) respectively. While the calcium polyhedra became more regular with pressure, the distortion of the phosphate tetrahedron remained unchanged. The size of the channel extending along the [001] direction represented the most compressible direction. The Ca2–Ca2 distance decreased from 3.982 to 3.897?Å on compression from 0.0001 to 4.72?GPa. The anisotropic compressional pattern may be understood in terms of the greater compressibility of the channel size over the polyhedral units. The reduction of the channel volume was measured by the evolution of the trigonal prism, having the Ca2–Ca2–Ca2 triangle as its base and the c lattice parameter as its height. This prism volume changed from 47.3?Å3 at room pressure to 44.78?Å3 at 4.72?GPa. Its relatively high bulk moduli, 86(3) GPa, indicated that the channel did not collapse with pressure and the apatite structure could remain stable at very high pressure.  相似文献   

12.
The authors report the results of X-ray diffraction (XRD) and geochemical studies on bastnaesites (lanthanum cerium fluoro-carbonate) hosted in alkali Kanigiri Granite of the Prakasam district in Andhra Pradesh, India. The XRD pattern of the investigated bastnaesite displays sharply-defined reflections. The observed d-spacings of the bastnaesite are in very close agreement with those published for bastnaesite standard in International Centre for Diffraction Data (ICDD) Card No. 11–340. The calculated unit cell parameters (a o ; c o ) and unit cell volume (V) of the studied bastnaesite (a o 7.1301–7.1413 Å, c o 9.7643–9.7902Å and V 429.8940–432.3875 Å3) are almost equal to values published for bastnaesite standard (c o 7.1290 Å, c o 9.7744 Å and V 430.19 Å3) in the relevant data card. Geochemical data of bastnaesite reveals high content of Ce (mean 27.22%) followed by La (mean 16.82%), Nd (mean 6.12%) and Pr (mean 1.91%). Compared to light REE (LREE) content (mean 437165 ppm), heavy REE (HREE) content (mean 5867 ppm) is drastically low, with unusually high LREE/HREE ratio (mean 80). The chondrite-normalised plot also exhibits drastic enrichment of LREE relative to HREE with pronounced negative Euanomaly (mean Eu/Eu* = 0.15). High (LREE) N / (HREE) N , (La/Lu) N , (La/Yb) N and (Ce/Yb) N ratios reveal higher fractionation of LREE relative to HREE. The rare earth element (REE) contents of the studied bastnaesite are very close to REE contents of bastnaesite hosted in alkali syenite from Madagascar. The presence of bastnaesite in Kanigiri Granite and soils derived from it enhances the scope of further exploration for bastnaesite in several bodies of alkaline rocks and alkali granitoids present along the eastern margins of the Cuddapah basin, Andhra Pradesh.  相似文献   

13.
ABSTRACT Gravity cores of Holocene sediments from a shallow ephemeral lake in the Coorong region (Pellet Lake, southeastern coastal Australia) show a mineral assemblage and sequence particular to its hydrology. The mineralogical sequence above an initial dolomitic siliciclastic sand reflects conditions of increasing salinity in the lower portions of the core (i.e. organic-rich aragonite to magnesite + hydromagnesite + aragonite) followed by a relative decrease in salinity (i.e. magnesite + aragonite + hydromagnesite to aragonite + hydromagnesite) in the upper portions of the core. This sequence is capped by ? 0.4 m of micritic dolomite and minor amounts of hydromagnesite, with the relative abundance of dolomite increasing upwards. Three stratigraphically and spatially distinct dolomite units (upper, lower and margin) are recognized using stable carbon and oxygen isotope data, unit cell calculations and MgCO3 mole per cent data of the dolomite. Detailed X-ray diffraction (XRD) analyses of samples with more than 80% dolomite shows that the dolomite is ordered. Average unit cell parameters, calculated from the XRD patterns, indicate that the upper dolomite unit has crystal lattices expanded in the co direction (co= 16.09 Å) relative to ideal dolomite (co= 16.02 Å) and contracted in the ao direction (ao= 4.796 Å) relative to ideal dolomite (ao= 4.812 Å). The mol fraction of MgCO3 in the upper dolomite shows up to 4.0 ±M 2.0 mole per cent excess Mg in the dolomite crystal lattice (calculated from XRD). This unusual dolomite crystal chemistry is probably generated by rapid precipitation from solutions which have greatly elevated Mg/Ca ratios. Transmission electron microscopy reveals that the upper dolomite has a heterogeneous microstructure which also suggests rapid precipitation from solution. The modulated microstructure found in calcium-rich dolomite is completely lacking. Dolomite ordering reflections are present in electron diffraction patterns, but are weak. Stable oxygen and carbon isotope values of the upper dolomite are tightly grouped (ave. δ18O ～+ 7.55%o, δ13C ～+ 4.10%o), yet show three upward-lightening oxygen cycles. The oxygen cycles correlate with three upward decreases in the calculated Mg content of the dolomite zone. These cycles may indicate the increased importance of rain-water dilution of the brine at times when the water in the lake was at its shallowest levels. Analyses of the lower dolomite and the margin dolomite suggest that these units precipitated more slowly from less evaporitic brines than the upper dolomite unit. The lower dolomite is close to stoichiometric, has less evaporitic stable isotope values than the upper dolomite, and has only a slightly expanded co-axis. The margin dolomite is Ca-rich, has a more homogeneous microstructure, and has expanded ao and co axes. The abundance of relatively soluble Mg-bearing phases, such as hydromagnesite and magnesite, may supply additional magnesium for the dolomitization of aragonite and calcite during subsequent diagenesis and burial of the sediment. This process may leave a finely laminated dolomicrite deposit which retains little, if any, evidence of evaporite minerals.  相似文献   

14.
江西永平铜矿矽卡岩矿物特征及其地质意义   总被引：4，自引：3，他引：1  
田明君  李永刚  万浩章  张宇  高婷婷 《岩石学报》2014,30(12):3741-3758
永平铜矿含矿岩石主要为绿帘石透辉石石榴石矽卡岩,这种岩石类型是与斑岩体有关的矽卡岩铜矿的典型赋矿岩石。通过对这一主要赋矿矽卡岩的研究,我们发现石榴石生长分为两个阶段:(1)早期石榴石:主要分布在石榴石颗粒核部,XAdr=1.0,主要以钙铁榴石为主,说明早期流体中可能含有较多的铁,是在较氧化条件下形成的;(2)晚期石榴石,沿石榴石裂隙重新成核或者在靠近流体通道的早期石榴石表面生长,出现震荡环带,XAdr=0.46~0.99,为钙铁-钙铝石榴石系列。石榴石发生变化的期间也形成新的矿物,如绿帘石、萤石、方解石和石英等。共存石榴石和绿帘石矿物中存在Fe3+-Al3+之间的替代,说明流体的氧逸度、组分浓度或aFe3+/aAl3+可能发生了变化。金属矿物也可能是在这一阶段形成的。永平铜矿矽卡岩从接触带到大理岩空间上有分带现象。从岩体到围岩的变化趋势为:石榴石含量减少,颜色存在红棕色-棕色-棕绿色-黄绿色-浅黄色的变化趋势;矿石品位降低,这与石榴石中Al2O3含量的变化较一致。我们认为这种变化是含矿热液对早期矽卡岩进行再交代改造的结果,表现为石榴石和绿帘石中Fe3+-Al3+含量的变化,并将Cu等金属沉淀下来。根据矽卡岩矿物的这些特征,在矿床勘探时,可依据棕色石榴石来追踪主矿体的位置。  相似文献   

15.
We study how deviations from spherical symmetry of a system, produced by angular momentum, and shear stress, modify the spherical collapse model parameters, as linear density threshold for collapse of the non-relativistic component (δc) and its virial overdensity (ΔV), in Einstein–de Sitter and ΛCDM models. We modify the spherical collapse model to take account of the shear term and angular momentum term. We find that the non-spherical terms change the non-linear evolution of the system and that the collapse stops “naturally” at the virial radius. Moreover, values of the linear overdensity parameter and of ΔV are modified with respect to the standard spherical collapse model.  相似文献   

16.
Dielectric data for volcanic scoria and basalt on the earth at microwave frequency are extremely sparse, and also crucial for volcanic terrains imaging, and development. In consideration of their similarity to lunar regolith (soils and rocks) in chemical and mineral composition, the dielectric data is significative for passive and active microwave remote sensing on the Moon. This study provides the data about the dielectric properties of three kinds of scoria and two kinds of basalt in China. The method put forward in this paper is also applicable for measuring the dielectric properties of dry rocks and other granular ground materials with low complex dielectric constants. Firstly, the authors measured the ε‘ and tanδ values of strip specimens prepared from the mixture of scoria or basalt powder and polythene with the resonant cavity perturbation method at 9370 MHz. Secondly, from the ε‘ and tang values of the mixture, the ε‘s and tanδs values of sofid scoria and basalt were calculated using Lichtenecker‘s mixture formulae. Finally, the effective complex dielectric constants, ε‘e and tanδs, of scoria at different bulk densities were calculated. The results have shown that the ε‘s and tang svalues of all solid basaltic materials measured (both solid basaltic scoria or basalt) are approximately 7 and 0.05,respectively. With increasing bulk density of scoria, the ε‘s and tanδs values of scoria increase significantly.  相似文献   

17.
High-pressure in situ X-ray diffraction experiment of Fe- and Al-bearing phase D (Mg0.89Fe0.14Al0.25Si1.56H2.93O6) has been carried out to 30.5 GPa at room temperature using multianvil apparatus. Fitting a third-order Birch–Murnaghan equation of state to the P–V data yields values of V 0 = 86.10 ± 0.05 Å3; K 0 = 136.5 ± 3.3 GPa and K′ = 6.32 ± 0.30. If K′ is fixed at 4.0 K 0 = 157.0 ± 0.7 GPa, which is 6% smaller than Fe–Al free phase D reported previously. Analysis of axial compressibilities reveals that the c-axis is almost twice as compressible (K c  = 93.6 ± 1.1 GPa) as the a-axis (K a  = 173.8 ± 2.2 GPa). Above 25 GPa the c/a ratio becomes pressure independent. No compressibility anomalies related to the structural transitions of H-atoms were observed in the pressure range to 30 GPa. The density reduction of hydrated subducting slab would be significant if the modal amount of phase D exceeds 10%.  相似文献   

18.
Experiments on the join Al2SiO5-“Mn2SiO5” of the system Al2O3-SiO2-MnO-MnO2 in the pressure/temperature range 10–20 kb/900–1050° C with gem quality andalusite, Mn2O3, and high purity SiO2 as starting materials and using /O2-buffer techniques to preserve the Mn3+ oxidation state had following results: At 20 kb/1000°C orange-yellow kyanite mixed crystals are formed. The kyanite solid solubility is limited at about (Al1.88Mn 0.12 3+ )SiO5 and, thus, equals approximately that on the join Al2SiO5-“Fe2SiO5” (Langer and Frentrup, 1973) indicating that there is no Jahn-Teller stabilisation of Mn3+ in the kyanite matrix. 5 mole % substitution causes the kyanite lattice constants a o, b o, c o, and V o to increase by 0.015, 0.009, 0.014 Å, and 1.6 Å3, resp., while α, β, γ, remain unchanged. Between 10 and 18 kb/900°C, Mn3+-substituted, strongly pleochroitic (emeraldgreen-yellow) andalusitess (viridine) was obtained. At 15 kb/900°C, the viridine compositional range is about (Al1.86Mn 0.14 3+ )SiO5-(Al1.56Mn 0,44 3+ )SiO5. Thus, Al→Mn3+ substitutional degrees are appreciably higher in andalusite than in kyanite, proving a strong Jahn-Teller effect of Mn3+ in the andalusite structure, which stabilises this structure type at the expense of kyanite and sillimanite and, thus, enlarges its PT-stability range extremely. 17 mole % substitution cause the andalusite constants a o, b o, c o, and V o to increase by 0.118, 0.029, 0.047 Å and 9.4 Å3, resp. At “Mn2SiO5”-contents smaller than about 7 mole %, viridine coexists with Mn-poor kyanite. At “Mn2SiO5”-concentrations higher than the maximum kyanite or viridine miscibility, braunite (tetragonal, ideal formula Mn2+Mn3+[O8/Si04]), pyrolusite and SiO2 were found to coexist with the Mn3+-saturated ky ss or and ss, respectively. In both cases, braunites were Al-substituted (about 1 Al for 1 Mn3+). Pure synthetic braunites had the lattice constants a o 9.425, c o, 18.700 Å, V o 1661.1 Å3 (ideal compn.) and a o 9.374, c o 18.593 Å3, V o 1633.6 Å3 (1 Al for 1 Mn3+). Stable coexistence of the Mn2+-bearing phase braunite with the Mn4+-bearing phase pyrolusite was proved by runs in the limiting system MnO-MnO2-SiO2.  相似文献   

19.
The high-pressure behavior of a vanadinite (Pb10(VO4)6Cl2, a = b = 10.3254(5), c = 7.3450(4) Å, space group P63/m), a natural microporous mineral, has been investigated using in-situ HP-synchrotron X-ray powder diffraction up to 7.67 GPa with a diamond anvil cell under hydrostatic conditions. No phase transition has been observed within the pressure range investigated. Axial and volume isothermal Equations of State (EoS) of vanadinite were determined. Fitting the P–V data with a third-order Birch-Murnaghan (BM) EoS, using the data weighted by the uncertainties in P and V, we obtained: V 0 = 681(1) Å3, K 0 = 41(5) GPa, and K′ = 12.5(2.5). The evolution of the lattice constants with P shows a strong anisotropic compression pattern. The axial bulk moduli were calculated with a third-order “linearized” BM-EoS. The EoS parameters are: a 0 = 10.3302(2) Å, K 0(a) = 35(2) GPa and K′(a) = 10(1) for the a-axis; c 0 = 7.3520(3) Å, K 0(c) = 98(4) GPa, and K′(c) = 9(2) for the c-axis (K 0(a):K 0(c) = 1:2.80). Axial and volume Eulerian-finite strain (fe) at different normalized stress (Fe) were calculated. The weighted linear regression through the data points yields the following intercept values: Fe a (0) = 35(2) GPa for the a-axis, Fe c (0) = 98(4) GPa for the c-axis and Fe V (0) = 45(2) GPa for the unit-cell volume. The slope of the regression lines gives rise to K′ values of 10(1) for the a-axis, 9(2) for the c-axis and 11(1) for the unit cell-volume. A comparison between the HP-elastic response of vanadinite and the iso-structural apatite is carried out. The possible reasons of the elastic anisotropy are discussed.  相似文献   

20.
Microsommite, ideal formula [Na4K2(SO4)] [Ca2Cl2][Si6Al6O24], is a rare feldspathoid that occurs in volcanic products of Vesuvius. It belongs to the cancrinite–davyne group of minerals, presenting an ABAB… stacking sequence of layers that contain six-membered rings of tetrahedra, with Si and Al cations regularly alternating in the tetrahedral sites. The structure was refined in space group P63 to R=0.053 by means of single-crystal X-ray diffraction data. The cell parameters are a=22.161?Å=√3a dav, c=5.358?Å=c dav; Z=3. The superstructure arises due to the long-range ordering of extra-framework ions within the channels of the structure. This ordering progressively decreases with rising temperature until it is completely lost and microsommite transforms into davyne. The order–disorder transformation has been monitored in several crystals by means of X-ray superstructure reflections and the critical parameters T c?≈?750?°C and β?≈?0.12 were obtained. The kinetics of the ordering process were followed at different temperatures and the activation energy was determined to be about 125?kJ?mol?1. The continuous order–disorder phase transition in microsommite has been discussed on the basis of a two-dimensional Ising model in a triangular lattice with nn (nearest neighbours) and nnn (next-nearest neighbours) interactions. Such a model was simulated using a Monte Carlo technique. The theoretical model well matches the experimental data; two phase transitions were indicated by the simulated runs: at low temperature only one of the three sublattices begins to disorder, whereas the second transition involves all three sublattices.  相似文献   

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