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  • 1
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    Mid-infrared spectroscopy of alkali feldspar samples for space application (2020)
    Springer Vienna
    Details
    Publication Date: 2023-06-23
    Description: Feldspars are major components of terrestrial planetary surfaces. For future space application and the setup of a comprehensive reference database, Na- and K-rich alkali feldspars, NaAlSi3O8 – KAlSi3O8, have been investigated by infrared reflectance spectroscopy. We related the feldspar spectra to the chemical composition and state of Al,Si order/disorder. The infrared measurements were analyzed with respect to band shifts and peak shapes using the autocorrelation function. Natural samples served as starting materials. Some samples were treated by the alkali exchange method to produce pure end-members, which were then heated to generate various states of Al,Si disorder. X-ray diffraction (XRD) methods served to determine the Al,Si distribution. Our autocorrelation allowed to differentiate between the compositional and the order/disorder influences seen in the spectra in the wavelength range between 7 μm up to 14 μm (1429 cm− 1 to 714 cm− 1). Space missions often analyze the surfaces of planetary bodies using remote sensing. Therefore, our results are essential to characterize and distinguish alkali feldspars on the surfaces of terrestrial planetary bodies like Mercury.
    Description: Deutsches Zentrum für Luft- und Raumfahrt https://doi.org/10.13039/501100002946
    Keywords: ddc:549 ; Alkali feldspars ; Infrared spectroscopy ; X-ray diffraction ; Al,Si distribution
    Language: English
    Type: doc-type:article
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  • 2
    Electronic Resource
    Electronic Resource
    Low-temperature coherent exsolution in alkali feldspars from high-grade metamorphic rocks of Sri Lanka (1993)
    Springer
    Contributions to mineralogy and petrology 114 (1993), S. 519-532 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract In the alkali feldspars of the amphibolite- and granulite-facies rocks of Sri Lanka, a late-stage, final exsolution event is observed which produced film lamellae and fine-scale spindles. These were investigated by optical, microprobe, single-crystal, transmission electron microscopy and atomic resolution microscopy techniques. The lamellae and spindles exsolved below the coherent solvus at temperatures as low as 300 to 350° C. Precession photographs and ARM micrographs show that the intergrowth is perfectly coherent. In sections ‖ (010) the rhombic section of the Pericline twins corresponds to analbite or high albite. The albite lamellae and spindles nucleated and grew at low temperatures in a metastable disordered structural state within a tweed-orthoclase matrix and became periodically twinned analbite or high albite, which subsequently developed only a slight increase in Al, Si order. The relationship between twin periodicity and lamellar width, predicted for coherent intergrowths by Willaime and Gandais (1972), is obeyed. In Or-rich grains, in which coherent exsolution is the only exsolution event, the film lamellae tend to be restricted to the rim, the fine-scale spindles to the centre of the grains. The films nucleated heterogeneously at grain boundaries and grew towards the grain centres. Fine-scale spindles probably nucleated homogeneously in the interior part of grains. Heterogeneous nucleation and coherent growth are not mutually exclusive.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00321756
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  • 3
    Electronic Resource
    Electronic Resource
    Two-feldspar geothermometry: a review and revision for slowly cooled rocks (1993)
    Springer
    Contributions to mineralogy and petrology 114 (1993), S. 510-518 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Recent improvements in the experimental and thermodynamic basis of two-feldspar geothermometry allow one to recover temperatures of coexistence more reliably. Some problems, however, persist: (1) the experimental solvi by Seck (1971a) and Elkins and Grove (1990) differ from each other; (2) it is not known to what extent Na−K−Ca exchange equilibrium is approached; (3) both solvi are probably metastable with regard to Al, Si order; (4) it is difficult to judge how closely high-temperature natural feldspars compare to this situation; (5) the thermodynamic treatment neglects phase transformations; (6) the temperature dependence of the Margules parameters used to model non-ideal mixing behaviour may not be linear; (7) it is not clear which expressions should be used to describe ideal activities. With these caveats in mind we treat the problem of retrograde resetting in high-grade metamorphic rocks that were slowly cooled under essentially dry conditions. Coexisting feldspars from such rocks commonly do not plot on a common isotherm. Thus temperatures derived from such pairs using any of the proposed two-feldspar geothermometers will necessarily be in error. We suggest that the non-equilibrium compositions result from retrograde intercrystalline K−Na exchange. This exchange continues after the plagioclase and alkali feldspar have already become essentially closed systems with respect to Al−Si exchange, which is a prerequisite for (Na,K)−Ca exchange. We use a modified version of the Fuhrman and Lindsley (1988) programme to reverse the K−Na exchange and derive concordant temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00321755
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  • 4
    Electronic Resource
    Electronic Resource
    Estimation of the Al,Si distribution of feldspars from the lattice translations Tr[110] and Tr[110] (1973)
    Springer
    Contributions to mineralogy and petrology 39 (1973), S. 141-156 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A method is proposed to estimate the Al,Si distribution of alkali feldspars from two lattice translations, called Tr[110] and Tr[1¯10], which are the repeat distances in the [110] and [1¯10] directions. The Al content t10 of the T10 tetrahedral site is estimated from Tr[1¯10], whereas Tr[110] measures t1m, the Al content of the T1m site. In order to simplify the estimation procedure, the line separation ψ=2θ (131)-2θ (1¯31) is given as a function of t10 and t10-t1m.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00375736
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  • 5
    Electronic Resource
    Electronic Resource
    Thermodynamic modelling of non-convergent ordering in orthopyroxenes: a comparison of classical and Landau approaches (1994)
    Springer
    Physics and chemistry of minerals 21 (1994), S. 555-560 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The excess Gibbs free energy due to non-convergent ordering is described by a Landau expansion in which configurational and non-configurational entropy contributions are separated: $$G^L = - hQ_t + \tfrac{1}{2}a^* (T - T_c^* )Q_t^2 + \tfrac{1}{n}e_n Q_t^n - TS_{conf \cdot }^{ord} $$ Neglecting higher order terms in Q t t, this expansion is formally equivalent to the reciprocal solution model for the distribution of Fe2+ and Mg over the non-equivalent M1 and M2 sites of orthopyroxenes: $$\begin{gathered} G^{ord} = - \tfrac{1}{2}[\Delta G_{exch}^0 - (L_{M1}^G - L_{M2}^G )X] + Q_t \hfill \\ {\text{ + }}\tfrac{1}{4}[\Delta G_{rec}^0 - (L_{M2}^G - L_{M1}^G )] + Q_t^2 {\text{ - }}TS_{{\text{conf}}^ \cdot }^{{\text{ord}}} \hfill \\ \end{gathered} $$ The Q t term describes a temperature and composition-dependent thermodynamic field that prevents the crystal from attaining full disorder at a finite temperature. The X term models the dependence of the field on composition. It causes the isotherms in a Roozeboom diagram X Fe M2 vs. X Fe M1 to be asymmetric. The Q t 2 term incorporates nearest-neighbour interactions. Higher order interactions are accounted for by the Q t n term, which is not routinely foreseen in the reciprocal solution model. The critical temperature T c * is interpreted as a ratio of enthalpy and entropy contributions to the free energy, ΔG rec 0 , of a reciprocal reaction $$T_c^* = \frac{{\Delta H_{rec}^0 - (L_{M1}^H + L_{M2}^H )}}{{\Delta S_{rec}^0 - (L_{M1}^S + L_{M2}^S )}}.$$ The comparison of Landau and classical approaches is extended to convergent ordering models which are shown to be incorporated in expressions for non-convergent ordering.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00203931
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  • 6
    Electronic Resource
    Electronic Resource
    Kinetic rate laws derived from order parameter theory III: Al, Si ordering in sanidine (1991)
    Springer
    Physics and chemistry of minerals 17 (1991), S. 563-568 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The time dependence of the ordering and disordering of Al and Si in sanidine is described within the framework of the kinetic rate laws developed in papers I and II of this series. It was found that the relevant order parameter Q t is homogeneous and non-conserved. The rate law is: $$\frac{{dQ_1 }}{{dt}} = - \frac{1}{\tau }exp(--\Delta G_a^* /k_B T)\frac{{\delta G_0 }}{{\delta Q_t }}.$$ The Gibbs free energy G 0 has no symmetry constraints and we find: $$G_0 (Q_t ) = --HQ_t + \tfrac{1}{2}a_t (T--T_c^t )Q_t^2 + \tfrac{1}{3}b_t Q_t^3 $$ with at/H = 0.0170 K−, T t c = 686 K for the approximation H ≫b t. The predicted temperature dependence of $$Q_t^{eq} = 1/0.017 (T--686 K)$$ for T ≫ 686 K agrees well with the experimental observations. The equivalent rate law is in the approximation b t = 0. $$Q_t^{eq} = 1/0.017 (T--686 K)$$ expressions for the time constant τ** are given. It is shown that the potential derived from the chemical rate law by Mueller (1967, 1969) closely corresponds to the quadratic approximation of the Gibbs free energy G0(Qt).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202235
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  • 7
    Electronic Resource
    Electronic Resource
    X-ray and electron-optical investigation of synthetic high-temperature plagioclases (1980)
    Springer
    Physics and chemistry of minerals 5 (1980), S. 255-277 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract High-temperature plagioclases NaAlSi3O8(Ab)-CaAl2Si2O8(An) have been prepared by dry devitrification of glasses. X-ray powder photographs were taken to follow the time-temperature dependence of indicators of structural state and to determine the lattice parameters of the plagioclases as well as their K-exchanged equivalents. Transmission electron microscopy (TEM) has been used to study the anorthite-type antiphase domain textures. The results are as follows: (1) TEM and X-ray powder data suggest to subdivide the high-temperature plagioclase series into three structural regions: (a) An0 to An30–40: monalbite/analbite to high albite-type structures, (b) An60–70 to An100: anorthite-type structures, (c) An30–40 to An60–70: transitional structures assumed to represent the early stages in the development of the structural complexities found in chemically intermediate low temperature plagioclases. (2) b-Antiphase domains typical for the anorthite-type structure could be imaged in samples ranging between An100 and An67.5, whereas c-antiphase domains have only been found in An90 and An100. The b-domains developed during isothermal crystallization, rather than cooling. The transition from the anorthite-type structure (S.G.I $$\bar 1$$ ) to an intermediate C $$\bar 1$$ -type structure at An60–70 appears to be a gradual one. (3) The relative contribution of various structural and chemical influences on the cell edges and angles is discussed in detail. It is shown that the nonlinear variation of γ with An content is due to incomplete Al,Si disorder in the high series.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00348574
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  • 8
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    The heat capacity of fayalite at high temperatures (2012)
    Mineralogical Society of America
    Details
    Publication Date: 2012-04-01
    Description: The high-temperature heat capacity of fayalite was reinvestigated using drop and differential scanning calorimetry. The resulting data together with drop calorimetry data taken from the literature were analyzed yielding CP J/(mol·K) = -584.388 + 129 440·T-1 - 3.84956·107·T-2 + 4.10143·109·T-3 + 98.4368·ln(T). This new CP polynomial is recommended for calculating phase equilibria involving fayalite at mantle conditions. Using thermal expansion coefficient and isothermal bulk modulus data from the literature, the isochoric heat capacity was calculated resulting in CV J/(mol·K) = - 217.137 + 63 023.1·T-1 - 2.15863·107·T-2 + 2.23513·109·T-3 + 51.7620·ln(T).
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 9
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    Mid-infrared spectroscopy of alkali feldspar samples for space application (2020)
    Springer
    Details
    Publication Date: 2020-07-30
    Description: Feldspars are major components of terrestrial planetary surfaces. For future space application and the setup of a comprehensive reference database, Na- and K-rich alkali feldspars, NaAlSi3O8 – KAlSi3O8, have been investigated by infrared reflectance spectroscopy. We related the feldspar spectra to the chemical composition and state of Al,Si order/disorder. The infrared measurements were analyzed with respect to band shifts and peak shapes using the autocorrelation function. Natural samples served as starting materials. Some samples were treated by the alkali exchange method to produce pure end-members, which were then heated to generate various states of Al,Si disorder. X-ray diffraction (XRD) methods served to determine the Al,Si distribution. Our autocorrelation allowed to differentiate between the compositional and the order/disorder influences seen in the spectra in the wavelength range between 7 μm up to 14 μm (1429 cm− 1 to 714 cm− 1). Space missions often analyze the surfaces of planetary bodies using remote sensing. Therefore, our results are essential to characterize and distinguish alkali feldspars on the surfaces of terrestrial planetary bodies like Mercury.
    Print ISSN: 0930-0708
    Electronic ISSN: 1438-1168
    Topics: Geosciences
    Published by Springer
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  • 10
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    Invariant relations between the moduli squares of reciprocal lattice vectors (2010)
    International Union of Crystallography
    Details
    Publication Date: 2010-08-29
    Print ISSN: 0108-7673
    Electronic ISSN: 2053-2733
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by International Union of Crystallography
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