共查询到20条相似文献,搜索用时 15 毫秒
1.
J. Garcia-Guinea P. D. Townsend L. Sanchez-Muñoz J. M. Rojo 《Physics and Chemistry of Minerals》1999,26(8):658-667
Laboratory driven ionic thermal exchange of alkali feldspars from K to Na produces samples which are strongly luminescent
in the ultraviolet region near 320 nm. The sites providing this luminescence are suggested as being correlated with the motion
of Na atoms along interface-interphases of the material (i.e. with Na-O bond fracture). The thermoluminescence peaks show
multi-order kinetics. Thermal preheatings of low albite sensitize the feldspar lattice with respect to thermoluminescence
generated by exposure to UV irradiation and heating produces a strong blue luminescence spread over the range 350 nm to 500 nm
band in feldspars. The upper temperature for thermoluminescence in feldspars is ∼300 °C, which is also the point where ionic
conductivity of albite (010) begins, but the 300 °C region is also the starting point of a large second glow peak in adularia.
Whilst it seems appropriate to link the Na motion to the 350–500 nm emission, it is unclear whether these changes are the
result of the large anisotropic thermal vibration of Na atoms or the massive Na jumps that occur when the lattice reaches
300 °C. A speculative model is considered in which the UV TL emissions of natural minerals are linked to different interface-interphases
(grain boundaries, exsolution limits, twinning planes, antiphase domains). Increased interface coherency energies are related
to the kinetic order and the spectral position of luminescence emission peaks.
Received: 3 December 1998 / Revised, accepted: 17 April 1999 相似文献
2.
D. R. Waldbaum 《Contributions to Mineralogy and Petrology》1967,17(1):71-77
Recent hydrofluoric acid solution calorimetric data are used to derive standard enthalpies and Gibbs free energies of formation of low-albite, high-albite, NaAlSi3O8 glass, microcline, sanidine, and KAlSi3O8 glass. The data are presented as high-temperature functions from 298.15 to 1400° K. 相似文献
3.
Structural energetics of the alkali feldspars have been studied using a “lattice” or structure energy model. Electrostatic energies, U e,for 20 well-refined, non-intergrown alkali feldspars were calculated using Bertaut's (1952) summation procedure and average about ?13,400 kcal/mol; the repulsive energies of the alkali site in each structure (~15 kcal/mol) were calculated using repulsive parameters for K-O and Na-O interactions estimated from bulk modulus data for NaF and KF and the exponential form of the repulsive potential. Using a procedure in which the position of the alkali cation was varied while the oxygen cage was kept fixed, structure energy gradients for the alkali sites of high albite and a hypersolvus Ab42Or58 structure were computed. In both cases, a broad structure energy well, elongated approximately parallel to c and subparallel to the observed split Na positions, was found. In both structures there is a single energy minimum corresponding closely with the observed single alkali positions. Comparison of U e values for the alkali feldspars with different K/Na ratios shows that intermediate compositions are predicted to be less “stable” than either endmember and that the potassic end-member is predicted to be less “stable” than the sodic one, assuming that all other factors contributiong to the free energies of each phase are approximately the same. Comparison of U e values for the high albite and low sanidine structures with different Al/Si distributions and a fixed tetrahedral framework indicates that the ordered charge distributions are 63.0 and 54.8 kcal/mol, respectively, more “stable” than the disordered distributions. Smaller, more realistic energy differences were obtained by using U evalues averaged from four separate calculations with a +3 charge on a different T site in each and with +4 charges on the other T sites. If, in addition, the charges on cations and oxygen are reduced to half their nominal formal charges, in agreement with Pauling's electroneutrality principle and the results of recent molecular orbital calculations on silicates, the predicted electrostatic energy differences are reduced to 3.6 and 1.6 kcal/mol, respectively. These calculations also indicate that the T1O site in the high albite structure energetically favors Al and that the Al/Si distribution determines the Na position within the alkali site. 相似文献
4.
The structural state of an alkali feldspar is determined by the nature of the distribution of Al and Si in the tetrahedral sites of the feldspar structure. This state is a function of a number of genetic controls including temperature, cooling rate, deformation, crystal size, and several chemical factors. Together these controls constitute a genetic regime. Identification of the structures of detrital feldspars may enable recognition of genetic regimes and be useful in provenance interpretation and mineral province definition. A 2-peak method of X-ray diffraction (XRD) determination as a variant of an earlier proposed 3-peak method of structural state determination is used in this study. Total analytical time for each determination is about 50–55 min per grain. Results of structural state identification of 126 detrital feldspars from Holocene stream sands derived from volcanic, plutonic and metamorphic rocks are presented in order to illustrate the application and potential of the technique. Detrital feldspars from the metamorphic rocks are all maximum microcline; those from the plutons range from orthoclase to microcline depending on the age of the pluton, whereas those from the volcanic rocks are sanidines. 相似文献
5.
T. F. W. Barth 《Mineralogy and Petrology》1965,10(1-4):14-33
Summary The crystalline variants of the alkali feldspars differ from each other in the pattern of Al/Si disorder. The interrelations of the several variants are graphically shown in Figs. 1, 2, and 3. In high albite thekind of disorder is different from that in any other alkali feldspar; therefore the transition high albitemonalbite is diffusive; but the transition monalbiteanalbite is displacive. See Fig. 10.The phase diagram of the system NaAlSi3O8–KAlSi3O8 is presented in Fig. 4. The volume relations of the mixed crystals (Figs. 5 and 8) indicate that albite exhibiting monoclinic symmetry at room temperature has a defect lattice (defect monalbite) with vacant Na sites. A vacant cation site behaves as if a large cation (for example K) were present; therefore the defect monalbite behaves like a mixed crystal with some K replacing Na.
With 10 Figures
Dedicated to ProfessorF. Machatschki on the occasion of his 70th birthday. 相似文献
Zusammenfassung Die verschiedenen kristallinen Modifikationen der Alkalifeldspate unterscheiden sich bezüglich der Art und Weise ihrer Al/Si-Verteilung. Die Interrelationen sind in den Abb. 1, 2 und 3 dargestellt. Im Hochalbit ist die Al/Si-Verteilung andersartig als in irgendeinem anderen Alkalifeldspat. Die meisten Alkalifeldspate haben eine zwifache Unendlichkeit von Variationsmöglichkeiten der Al/Si-Verteilung (entsprechend der in Abb. 2 eingezeichneten Ebene), Hochalbit aber steht einzig da und weist eine dreifache Unendlichkeit von Möglichkeiten auf. Infolgedessen entspricht dem Übergang HochalbitMonalbit ein diffuser Umwandlungsmechanismus, dem Übergang MonalbitAnalbit aber ein displaciver (Abb. 10).Das Phasendiagramm des Systems NaAlSi3O8–KAlSi3O8 ist in Abb. 4 dargestellt. Die Volumverhältnisse der Mischkristalle (Abb. 5 und 8) deuten darauf hin, daß der bei gewöhnlicher Temperatur monokline Albit ein defektes Gitter hat (= defekter Monalbit mit teilweise unbesetzten Na-Punktlagen). Die Wirkung einer unbesetzten Kation-Punktlage im Gitter ist der Wirkung eines großen Kations (z. B. Kalium) gleich; hierdurch erklärt sich die Tatsache, daß der defekte Monalbit die Eigenschaften eines etwas K-haltigen Mischkristalls nachahmt.
With 10 Figures
Dedicated to ProfessorF. Machatschki on the occasion of his 70th birthday. 相似文献
6.
George D. Guthrie Jr. David R. Veblen 《Contributions to Mineralogy and Petrology》1991,108(3):298-304
Partially turbid alkali feldspars from hydrothermally altered Tertiary granites on the Isle of Skye (the Red Hills granites)
were studied using light microscopy, scanning and transmission electron microscopies, and energy-dispersive X-ray spectroscopy.
Limpid cores and turbid rims of individual crystals were compared to determine the causes of the turbidity. The limpid cores
were cryptoperthitic, with lamellar widths of 0.1–0.3 μm. In contrast, the turbid rims contained K-rich and Narich areas coarsened
to >0.5 μm. Turbid regions contained abundant inclusions, whereas limpid regions did not. Two generations of turbidity were
recognized. Feldspars from the Beinn an Dubhaich granite, a granite with near-normal values for 18O/16O possessed limpid cores surrounded by turbid rims that cast a reddish-brown hue in transmitted light. When viewed in darkfield
light microscopy, the regions with the reddish-brown turbidity were blue. This is consistent with the hypothesis that the
cloudy appearance of these turbid regions arises from the scattering of light by micrometerto submicrometer-sized inhomogeneities
in refractive index caused by fluid-filled cavities. Feldspars from the Loch Ainort granite, a granite with low values for
18O/16O possessed limpid and reddish-brown-turbid cores surrounded by turbid rims that cast a blackish hue in transmitted light.
Ion thinning of the turbid areas produced an abundance of small holes (≤1–2 μm) apparently the remains of fluid inclusions.
Transmission electron microscopy revealed that some holes from regions of reddish-brown turbidity contained non-feldspar material,
including halite and metal-rich phases of various compositions. In contrast, blackish turbid regions contained cavities filled
with alteration products, such as kaolinite. Hence, the feldspars from granites on the Isle of Skye apparently record interactions
with at least two fluids: a saline fluid (possibly a late-stage magmatic fluid) and a meteoric fluid. 相似文献
7.
Summary Feldspar phenocrysts in alkali rhyolite from Oki-Dogo island in the Sea of Japan show mantled textures with cores of anorthoclase and rims of sanidine. These feldspars were examined by electron microscopy, X-ray diffraction and X-ray microanalysis. Anorthoclase first crystallized, then was partially resorbed, and finally sanidine overgrew on the anorthoclase. Saw-tooth or comb-like interfaces between the cores and rims were likely formed at the magmatic stage of resorption and overgrowth. Optically perthitic intergrowths appear in thin sections cutting saw-tooth or comb-like interfaces of the mantled feldspars. The sanidine preserves primary cryptoperthitic textures of a periodicity smaller than 10 nm, which are considered to have been produced by subsolidus exsolution after the resorption event ended. The anorthoclase has no exsolution texture under an electron microscope.
With 6 Figures 相似文献
Feldspatkristalle in Alkali-Rhyolith von der Insel Oki-Dogo, Japan
Zusammenfassung Feldspatkristalle in Alkali-Rhyolith von der Oki-Dogo Insel im Japanischen Meer zeigen ummantelte Texturen mit Kernen von Anorthoklas und Rändern von Sanidin. Diese Feldspate wurden mit Elektronenmikroskopie, Röntgendiffraktion und Mikrosondenanalyse untersucht. Anorthoklas kristallisierte zuerst, wurde dann teilweise resorbiert und schließlich wuchs Sanidin über den Anorthoklas. Sägezahn- und Kamm-ähnliche Grenzen zwischen Kernen und Rändern wurden wahrscheinlich wahrend des magmatischen Stadiums von Resorption und Überwachsung gebildet. Unter dem Mikroskop erkennt man, daß perthitische Verwachsungen durch Sägezahn- oder Kamm-artige Grenzen der ummantelten Feldspäte hinwegsetzen. Der Sanidin erhellt primäre kryptoperthitische Texturen mit einer Periodizität von > 10 nm, die als Produkte einer Subsolidus-Entmischung nach der Resorption interpretiert werden. Anorthoklas läßt unter dem Elektronenmikroskop keine Entmischungstexturen erkennen.
With 6 Figures 相似文献
8.
The petrological significance of misorientations between grains 总被引:4,自引:1,他引:4
J. Wheeler D. Prior Z. Jiang R. Spiess P. Trimby 《Contributions to Mineralogy and Petrology》2001,141(1):109-124
Misorientation analysis quantifies microstructural features in tectonites, metamorphic and igneous rocks, and allows hypotheses on their formation to be tested. The misorientation between two lattices can be expressed by a rotation axis and rotation angle. For lattices with symmetry, it is conventional to take the minimum angle that enables one lattice to be rotated into the other. For a group of lattice measurements two types of misorientation distribution can be calculated. Selecting random pairs of grains gives the random-pair misorientation distribution. Selecting neighbouring pairs gives the neighbour-pair misorientation distribution. The forms of both distributions are visualised using histograms or cumulative frequency diagrams. They are strongly influenced by any overall crystallographic preferred orientation and by intrinsic crystal symmetry. In many rocks, the random-pair misorientation distribution and neighbour-pair misorientation distribution are statistically significantly different (quantified using the Kolmogorov-Smirnov test). Differences between the random-pair misorientation distribution and neighbour-pair misorientation distribution imply that adjacent grains have physically interacted or are inherited from a precursor microstructure. Interactions include (1) reduction in surface energy by lattice alignment. We show this may have occurred in garnet clusters in schist, and olivine in a cumulate. It is well-known in metals and may be a common geological process. (2) Nucleation, where those nuclei have influenced the orientation of adjacent nuclei. (3) Mechanical rotations of facetted grains in compacting crystal mushes, so that faces become parallel. (4) Growth twinning. Inheritance includes (1) subgrain rotation recrystallisation in tectonites deforming by crystal plastic processes. (2) Mechanical and transformation-related twinning. (3) Domainal microstructures, e.g. where grains have formed from a few large original grains, may give rise to spurious correlations when the orientation data cover more than one domain. With this proviso, misorientation analysis can be used to investigate many important microstructural processes. 相似文献
9.
Martin R. Lee Mark E. Hodson Maureen MacKenzie Caroline L. Smith 《Geochimica et cosmochimica acta》2008,72(20):4962-4975
Our ability to identify thin non-stoichiometric and amorphous layers beneath mineral surfaces has been tested by undertaking X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) work on alkali feldspars from pH 1 dissolution experiments. The outcomes of this work were used to help interpret XPS and TEM results from alkali feldspars weathered for <10,000 years in soils overlying the Shap Granite (north-west England). The chemistry of effluent solutions indicates that silica-rich layers a few nanometers in thickness formed during the pH 1 experiments. These layers can be successfully identified by XPS and have lower Al/Si, Na/Si, K/Si and Ca/Si values than the outermost ∼9 nm of unweathered controls. Development of Al-Si non-stoichiometry is coupled with loss of crystal structure to produce amorphous layers that are identifiable by TEM where >∼2.5 nm thick, whereas the crystallinity of albite is retained despite leaching of Na to depths of tens to hundreds on nanometers. Integration of XPS data over the outermost 6-9 nm of naturally weathered Shap feldspars shows that they have stoichiometric Al/Si and K/Si ratios, which is consistent with findings of previous TEM work on the same material that they lack amorphous layers. There is some XPS evidence for loss of K from the outermost couple of nanometers of Shap orthoclase, and the possibility of leaching of Na from albite to greater depths cannot be excluded using the XPS or TEM results. This study demonstrates that the leached layer model, as formulated from laboratory experiments, is inapplicable to the weathering of alkali feldspars within acidic soils, which is an essentially stoichiometric reaction. 相似文献
10.
Etching of alkali feldspar cleavage fragments with hydrofluoric acid vapor, followed by study of the surfaces by scanning electron microscopy (SEM), is a simple and rapid technique for characterizing the microtextures of crypto- and microperthites. This technique has a number of advantages over conventional transmission electron microscopy (TEM) including ease of sample preparation and the large areas of crystals which can be imaged. Alkali feldspars studied by the method can yield important information on the cooling history of igneous and metamorphic rocks, fluid-feldspar interactions and the morphology and microstructures of albite exsolution lamellae. Some of these applications are illustrated by examples of etched crypto- and micro-perthites from the Klokken layered syenite, south Greenland and the Shap granite, north-west England. 相似文献
11.
Alkali feldspar cleavage fragments from the Klokken layered syenite, South Greenland, were heated to 700°C at 0.1 GPa in 99% H2
18O for 75 h. These samples were then polished and imaged by ion microprobe for 18O. The feldspars were known to contain areas of pristine, braid micro-perthite which were not turbid and areas of deuteric patch perthite which were turbid. Turbidity is related to the presence of micropores in the feldspars. On imaging the grain, it was found that the 18O had penetrated into the parts of the grain which were microporous and not into the pristine areas. Micropores are therefore responsible for rendering the feldspars permeable as well as porous. The implications of micropermeable feldspars in several areas of geology are discussed. 相似文献
12.
Christos Evangelakakis Herbert Kroll Gerhard Voll Hans-Rudolf Wenk Hu Meisheng Jürgen Köpcke 《Contributions to Mineralogy and Petrology》1993,114(4):519-532
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. 相似文献
13.
Miriam Kastner 《Geochimica et cosmochimica acta》1974,38(4):650-653
About 5 per cent of all feldspars in sediments are authigenic. This amounts to 0·94 per cent of the total sedimentary mass. At least 2.1 × 1018 kg Na and 3.4 × 1018kg K have been removed from sea water by reconstitution of authigenic feldspars in the total mass of surviving sediments. Consequently, 9.3 × 1019 moles CO2 have been released by the formation of authigenic albite and 8.8 × 1019 moles CO2 by the formation of authigenic K-feldspar. 相似文献
14.
A transmission electron microscope study of intracrystalline boundaries between two perthites of markedly different composition in composite crystals, one a tenary mesoperthite (Or26Ab52An22, initially a homogeneous potassian monalbite) the other a more potassic cryptoperthite (Or61Ab33An6, initially a homogeneous sodian sanidine), shows that the two perthites are in nearly parallel intergrowth. Most boundaries examined were of (hkO) type; (010) boundaries are straight, whereas other (hkO) boundaries are curved or stepped. Exsolution occurred first in the potassian monalbite (mesoperthite) and was unaffected by the boundary. Subsequent exsolution in the sodian sanidine (cryptoperthite) was affected by the boundary, but for up to only a few micrometers. Exsolution occurred by heterogeneous nucleation and growth of oligoclase on and from the intracrystalline boundary. At almost the same time the rest of the volume of sanidine exsolved by spinodal decomposition. 1–2 μm from the boundary in the intervening K-rich matrix of the sodian sanidine, further exsolution occurred by homogeneous nucleation. Time — temperature — transition curves for continuous cooling have been devised to account for the unusual complexity of the exsolution texture. Except in such exceptional circumstances as the example studied, the initial exsolution in high-temperature alkali feldspars of intermediate composition, unlike other minerals, probably does not occur by nucleation, but only by spinodal decomposition. 相似文献
15.
The mechanism of cation and oxygen isotope exchange in alkali feldspars under hydrothermal conditions 总被引:2,自引:1,他引:2
Dominik R. D. Niedermeier Andrew Putnis Thorsten Geisler Ute Golla-Schindler Christine V. Putnis 《Contributions to Mineralogy and Petrology》2009,157(1):65-76
The mechanism of re-equilibration of albite in a hydrothermal fluid has been investigated experimentally using natural albite
crystals in an aqueous KCl solution enriched in 18O at 600°C and 2 kbars pressure. The reaction is pseudomorphic and produces a rim of K-feldspar with a sharp interface on
a nanoscale which moves into the parent albite with increasing reaction time. Transmission electron microscopy (TEM) diffraction
contrast and X-ray powder diffraction (XRD) show that the K-feldspar has a very high defect concentration and a disordered
Al, Si distribution, compared to the parent albite. Raman spectroscopy shows a frequency shift of the Si-O-Si bending vibration
from ~476 cm−1 in K-feldspar formed in normal 16O aqueous solution to ~457 cm−1 in the K-feldspar formed in 18O-enriched solution, reflecting a mass-related frequency shift due to a high enrichment of 18O in the K-feldspar silicate framework. Raman mapping of the spatial distribution of the frequency shift, and hence 18O content, compared with major element distribution maps, show a 1:1 correspondence between the reaction rim formed by the
replacement of albite by K-feldspar, and the oxygen isotope re-equilibration. The textural and chemical characteristics as
well as the kinetics of the replacement of albite by K-feldspar are consistent with an interface-coupled dissolution-reprecipitation
mechanism. 相似文献
16.
A.E. Beswick 《Geochimica et cosmochimica acta》1973,37(2):183-208
K and Rb distributions between aqueous alkali chloride vapour phase (0.7 molar) and coexisting phlogopites and sanidines have been investigated in the range 500 to 800°C at 2000 kg/cm2 total pressure.Complete solid solution of RbMg3AlSi3O10(OH)2 in KMg3AlSi3O10(OH)2 exists at and above 700°C. At 500°C a possible miscibility gap between approximately 0.2 and 0.6 mole fraction of the Rb end-member is indicated.Only limited solid solution of Rb AlSi3O8 in KAlSi3O8 has been found at all temperatures investigated.Distribution coefficients, expressed as in solid/(Rb/K) in vapour, are appreciably temperature-dependent but at each temperature are independent of composition for low Rb end-member mole fractions in the solids. The determined values and their approximate Rb end-member mole fraction () ranges of constancy are summarized as follows: (°C)
(°C)T | ||||
500 | 0–0.2 | 0–0.07 | ||
700 | 0–0.2 | 0–0.1 | ||
800 | 0–0.2 | 0–0.1 |