Thermally activated electron delocalization in deerite     

G. Amthauer  K. Langer  M. Schliestedt 《Physics and Chemistry of Minerals》1980,6(1):19-30

The ⁵⁷Fe Mössbauer spectra of deerites of different chemical composition, taken at several temperatures, show that Fe²⁺ and Fe³⁺ occupy all the six-coordinated lattice sites with a preference of Fe³⁺ probably for the M(1) to M(3) positions, and a preference of Fe²⁺ probably for the M(4) to M(6) and the M(7) to M(9) sites. The room and high temperature spectra reveal absorption patterns due to thermally activated Fe²⁺ → Fe³⁺ electron delocalization. The extent of electron delocalization is dependent on the chemical composition, e.g., the amount of ions (Mg, Mn, Al) substituting for Fe.  相似文献   

Low temperature spectral studies of Mn3+-bearing andalusite and epidote type minerals in the range 30000–5000 cm−1     

Smith  G.  Hålenius  U.  Langer  K. 《Physics and Chemistry of Minerals》1982,8(3):136-142

Polarized absorption spectra of natural piemontite (Ca_1.802Mn ²⁺_0.178 Mg_0.025) (Mn ³⁺_0.829 Fe ³⁺_0.346 Al_1.825) [(Si_2.992Al_0.008) O₁₂OH], viridine (Al_1.945Mn ³⁺_0.033 Fe ³⁺_0.063 Mg_0.003) [O|Si_0.970 O₄], and kanonaite (Al_1.291Mn ³⁺_0.682 Fe ³⁺_0.019 ) [O|Si_1.006 O₄] were measured at 295 and ca. 100 K. For piemontite, lowering the temperature resulted in a sharpening of broad bands in the 10 000–25 000 cm⁻¹ region supporting their assignment to single ion Mn³⁺ in M3 non-centrosymmetric sites.

Alternatively, in kanonaite, temperature behaviour pointed to a slightly stronger influence of vibronic coupling on strong bands near 16 000 and 22 000 cm⁻¹, which supported an interpretation of Mn³⁺ in nearly centrosymmetric M1 sites. Measurements at ca. 100 K show pronounced fine structure in the viridine spectra which is attributed to Fe³⁺. The ɛ values for Mn³⁺ spin-allowed bands in the three minerals lie in the range 18 to 227 [1·g-atom⁻¹·cm⁻¹].

For the same band and polarisation, ɛ values in Mn³⁺-bearing andalusite-type minerals viridine and kanonaite are the same, which indicates an absence of strong magnetic coupling effects between Mn³⁺ ions in the andalusite type structure down to ca. 100 K.

In silicates, the high ɛ values for Mn³⁺ spin-allowed bands, in comparison to those obtained for Fe²⁺ spin-allowed bands from sites of “similar distortion”, is attributed to a higher degree of covalency in the Mn³⁺-O bonds compared to the Fe²⁺-O bonds, as a result of the higher valence state of manganese.

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Synthetic Mn3+-kyanite and viridine, (Al2-xMn x 3+ ) SiO5, in the system Al2O3-MnO-MnO2-SiO2     

I. Abs-Wurmbach  Prof. Dr. K. Langer 《Contributions to Mineralogy and Petrology》1975,49(1):21-38

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 (Al_1.88Mn _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 ų, resp., while α, β, γ, remain unchanged. Between 10 and 18 kb/900°C, Mn³⁺-substituted, strongly pleochroitic (emeraldgreen-yellow) andalusite_ss (viridine) was obtained. At 15 kb/900°C, the viridine compositional range is about (Al_1.86Mn _0.14 ³⁺ )SiO₅-(Al_1.56Mn _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 ų, 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 ų (ideal compn.) and a _o 9.374, c _o 18.593 ų, V _o 1633.6 ų (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   

Rheologische und modellmechanische Grundlagen für tektonische Experimente     

Privatdozent Wiss. Direktor Dr. Michael Langer 《International Journal of Earth Sciences》1972,61(3):806-823

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Water in microcrystalline quartz of volcanic origin: Agates   总被引：2，自引：0，他引：2  

O. W. Flörke  B. Köhler-Herbertz  K. Langer  I. Tönges 《Contributions to Mineralogy and Petrology》1982,80(4):324-333

Agates of volcanic origin, containing the different quartz species, fibrous, length-fast chalcedony (CH), granular fine quartz (FQ), and fibrous, length-slow, to lepidospheric quartzine (QN), have been investigated to evaluate possible relations between microstructure, i.e. crystallite size and texture, refractive indices, densities, contents of trace elements and of water, as well as dehydration behaviour. By means of near infrared spectroscopy, total water contents , could be differentiated quantitatively into contents of molecular water, , and silanole-group water, . Despite the low total water contents of the agates studied ( between 1 and 2 wt.%), near infrared spectroscopy results in reliable data on and .Wall-layering CH consists of fibrous quartz crystals and exhibits higher C-ratios, , than horizontally layered FQ which consists predominantly of granular quartz crystals (C _CH=0.45±0.11 (N=6), C _FQ=0.36±0.10 (N=4). This result is interpreted to be due to analogy with the behaviour of C-ratios in fluid phase-deposited opals-AN (hyalithe) and liquid phase-deposited opals-AG (non-crystalline opal) or -CT (common opal) (Langer and Flörke 1974).Translucent layers of CH show mostly lower refractive indices, when measured parallel than when measured perpendicular to the axes of the quartz fibers. The same is true for milky layers of CH. Crystallite sizes are smaller in the latter than in the former.For all samples studied, exists a positive correlation between at% (1/2Ca+1/2Mg+Na+K+Li) and at% (Al³⁺+Fe³⁺). This indicates that at least parts of (A1³⁺+ Fe³⁺) substitute for Si in the quartz structure. The charge is balanced by incorporation of di- and mono-valent cations in structural interstices. When the quantity at % H⁺, as obtained from , is included into the sum at% (1/2 Me²⁺+Me⁺), the above correlation is destroyed. This result could be indicative for a strong concentration of the Si-OH groups in the surface of the quartz microcrystallites.  相似文献   

Hydrogen in some natural garnets studied by nuclear reaction analysis and vibrational spectroscopy     

J.?MaldenerEmail author  A.?H?sch  K.?Langer  F.?Rauch 《Physics and Chemistry of Minerals》2003,30(6):337-344

A suite of 11 gem-quality, optically completely clear garnet crystals with a broad variety of compositions in the space of the end members pyrope–almandine–spessartine–grossular–andradite–goldmanite were analyzed for trace amounts of “water” by nuclear reaction analysis, NRA, based on the reaction ¹H(¹⁵N, αγ)¹²C, and by single-crystal absorption spectroscopy in the ν_OH vibrational range using microscope-FTIR-spectroscopic methods. The aim was to establish a calibration of the highly sensitive IR method with high areal resolution for “water” determination in garnets, by studying garnets of a wide compositional range, and to check for compositional dependencies of the integral molar absorptivities of the “water” component, ?_int[1mol_H2O^?1cm^?2], in the nominally “water”-free garnets. The results of NRA show a broad variation of water contents in the range (14 ± 3) to (950 ± 80) wt ppm_H2O, the values being low and very high for the garnet solid solutions (PyrAlm)_SS and close-to-end-member Gross_SS, respectively. There were no indications of inhomogeneities in the OH distribution, except possibly for one of the garnets (grossular, variety hessonite, from Tanzania). The quantitative evaluation of the complex ν_OH spectra, which showed similar shape only for members of the (PyrAlm)_SS, yielded integral absorption coefficients, α_int (cm^?2), which allowed the calculation of integral molar absorptivities, ?_int, using the “water” values of NRA. The ?_int values obtained varied in a wide range but with no obvious correlation with the composition of the garnet except for the extremely high values, in the 10⁴ range, of the two specimen with compositions close to end-member grossular. In all other garnets, ?_int was in the 10³ range with an average of ?_int=3630±1580[1mol_H2O^?1cm^?2]. Therefore, this value is proposed for the use in routine “water” determinations of compositionally different garnets by the micro-IR method, except for garnets near to end-member grossular.  相似文献   

Long-term observation of volcanic tremor on Stromboli volcano (Italy): A synopsis     

Horst Langer  Susanna Falsaperla 《Pure and Applied Geophysics》1996,147(1):57-82

The features of seismic activity on Stromboli are discussed and compared in terms of their relationship with the main changes of volcanic activity from 1990 to 1993.We considered a statistical approach for our data analysis. Cluster analysis was used to seek out classes of spectra which might characterize the condition of the volcanic system. The classes we have found provide insights into a scenario which evolves through different phases of volcanic activity, from paroxysms to low activity. We show that episodes of lava effusion and lava fountaining are heralded by variations in the spectral features of tremor after a preparation time. This result highlights the importance of tremor, and reveals that long-term observations are key to examine slow modifications in a volcanic system such as Stromboli, characterized by open conduits, and persistent explosive activity.  相似文献   

Pressure-induced (Al,Si)[4]-ordering in dioctahedral micas?     

Susanne Flux  Niranjan D. Chatterjee  Klaus Langer 《Contributions to Mineralogy and Petrology》1984,86(3):294-297

Pure, synthetic 2M₁-muscovites (Ms) and 2M₁-paragonites (Pg) prepared at 7, 13.5, and 18 kbar have been subjected to careful X-ray powder diffractometry and IR powder spectrometry. The results of X-ray studies show that the lattice constants of these micas are independent of the pressure employed in synthesizing them. Similarly, the IR powder spectra of Ms and Pg remain unaffected by the synthesis pressure. Neither the Al^[4]-O-Al^[4] vibrations decrease in relative intensity nor do the Si-O-Al^[4] vibrations increase in intensity with increasing pressure of synthesis, as they should, if pressure-induced (Al, Si)^[4] ordering had been operative. Finally, the v _OH bands in Ms and Pg are also found to retain their fine structural details, regardless of the pressures employed in synthesizing these phases. In particular, the half widths of v _OH in these (Al,Si)^[4]-disordered micas remain constant at around 60 cm⁻¹, compared to ∼ 10 cm⁻¹ in (Al,Si)^[4]-ordered mica margarite. In the light of this study, shortening of the b lattice parameter and progressive (Al,Si)^[4] ordering with increasing pressure of synthesis of muscovites reported by Velde (1980) would appear to be anomalous. Consequently, any discussion of the effect of (Al,Si)^[4] ordering on the stability of muscovite is a moot point at present.  相似文献   

Single crystal infrared spectra in the range of OH fundamentals of paragenetic garnet,omphacite and kyanite in an eklogitic mantle xenolith     

A. Beran  K. Langer  M. Andrut 《Mineralogy and Petrology》1993,48(2-4):257-268

Summary Single crystals of paragenetic garnet (gt), omphacite (cpx) and kyanite (ky) were isolated from an eclogite xenolith from the Zagadochnaya kimberlite, Yakutia (grospydite Z13) and studied by polarized FTIR-microspectrometry in the OH valence vibrational region and by microprobe analyses. The coexisting minerals are homogeneous with respect to major and minor elements and have compositions near gross₄₉pyr₂₆alm₂₀uvar₄ (gt), jad₄₅dio₄₇hed₆kos₂ (cpx) and ky_>97. Single crystal spectra show one _OH-band for gt at 3630 cm^–1 (halfwidth ca. 100 cm^–1) which is very likely caused by vibrations of tetrahedral (OH)₄-^4– clusters replacing SiO₄ ^4– tetrahedra. Cpx shows one strong, but weakly pleochroic band at 3464 cm^–1 (halfwidth ca. 160 cm^–1) and a weak satellite band centered at 3620 cm^–1) with a distinct pleochroism. Ky OH spectra exhibit two sets of weak sharp pleochroic bands, a triplet, characteristic for high pressure ky, at 3439, 3410, 3387 cm^–1) and a doublet at 3279, 3264 cm^–1) (halfwidths ca. 10 cm^–1) From integral and linear absorbances in the unpolarized spectra defect-hydroxyl contents in the three coexisting minerals were estimated and found near O.OX wt% H₂O. The distribution scheme of hydrogen in the paragenetic minerals was evaluated to be c^ky < c^cpx < c^gt.

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Einkristall Infrarotspektren im Bereich der OH Grundschwingungen einer Granat-Omphacit-Kyanit Paragenese in einem eklogitischen Mantelxenolith

Zusammenfassung Aus einer Granat (Gt)-Omphacit (Cpx)-Kyanit (Ky) Paragenese eines Eklogit Xenoliths aus dem Zagadochnaya Kimberlit, Jakutien (Grospydit Z13), wurden Einkristalle isoliert und mit polarisierter FTIR-Mikrospektrometrie im OH Valenzschwingungsbereich und mit der Elektronenstrahl-Mikrosonde untersucht. Die koexistierenden Minerale sind hinsichtlich ihrer Haupt- und Nebenelemente homogen und haben Zusammen setzungen von etwa Gross⁴⁹Pyr²⁶Alm²⁰Uvar₄ (Gt), Jad₄₅Dio₄₇Hed₆Kos₂ (Cpx) and Ky_>97 Einkristallspektren von Gt zeigen eine _OH-Bande bei 3630 cm^–1) (Halbwerts breite ca. 100 cm^–1) die wahrscheinlich von Schwingungen tetraedrischer (OH)₄ ^4– Gruppen, die SiO₄ ^4– Tetraeder ersetzen, herrührt. Cpx zeigt eine starke, aber schwach pleochroitische Bande bei 3464 cm^–1 (Halbwertsbreite ca. 160 cm^–1) and eine schwache, deutlich pleochroitische Satellitenbande bei 3620 cm^–1) Ky OH Spektren zeigen zwei Gruppen von schwachen, scharfen pleochroitischen Banden, ein fur Hochdruck Ky charakteristisches Bandentriplett bei 3439, 3410, 3387 cm^–1) and ein Bandendublett bei 3279, 3264 cm^–1) (Halbwertsbreiten ca. 10 cm^–1) Aus den integralen and linearen Extinktionen der nicht-polarisierten Spektren wurde der Defekt-Hydroxyl Gehalt der drei koexistierenden Minerale abgeleitet and mit O.OX Gew% H₂O festgelegt. Das Verteilungsschema des Wasserstoffs kann in der Mineralparagenese mit c^Ky < c^Cpx c^Gt angegeben werden.

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Dedicated to Prof. Dr. J. Zemann on the occasion of his 70th birthday

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With 3 Figures  相似文献   

Titanium substitution and OH-bearing defects in hydrothermally grown pyrope crystals     

V. M. Khomenko  K. Langer  A. Beran  M. Koch-Müller  T. Fehr 《Physics and Chemistry of Minerals》1994,20(7):483-488

A series of Ti-substituted pyrope crystals was synthesized in the system MgO-(Na₂O)-Al₂O₃-TiO₂-SiO₂-H₂O at P_H20 = P_tot between 25 and 30 kbars and 975 and 1000° C, using graphite heated piston-cylinder devices. The crystals, ranging up to 500 m in diameter, were studied by X-ray, electron-microprobe and FTIR-microscope spectrometric techniques. The pyrope crystals were colourless when hem/mt or mt/wu buffers were used during the synthesis, and pale blue with the wu/iron buffer and in unbuffered runs. Sodium was not found in the synthetic crystals, titanium was always near 0.06 Ti atoms pfu, independent on the Ti-excess used in the starting material. A substitution Al_2+[6]+Si_4+[4]+4O_2-= Ti_4+[6]+_[4]+[(OH)₃O^^5-, providing charge balance for octahedral Ti⁴⁺-substitution is found to be compatible with all properties (number, widths, position, integrated intensity) of the stretching vibrations of defect hydroxyls, which have energies 3684, 3568, 3525 cm^-1.This work was made possible through a research fellowship, generously provided by the Alexander von Humboldt-Stiftung, Bonn, Bad Godesberg, to V.M.K.  相似文献