Spinodal decomposition in alkali feldspar studied by atom probe tomography

Petrishcheva, Elena; Tiede, Lisa; Schweinar, Kevin; Habler, Gerlinde; Li, Chen; Gault, Baptiste; Abart, Rainer

doi:10.1007/s00269-020-01097-4

Cited by 13 publications

(11 citation statements)

References 49 publications

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“…Generally, the crystal structure of alkali feldspar contracts with a compositional shift from K-rich towards more Na-rich compositions, where the effect is largest in the direction of the crystallographic a axis and less pronounced parallel to the crystallographic b and c axes (Kroll et al, 1986;Angel et al, 2012). It is known from earlier work (Petrishcheva et al, 2014;Petrovic, 1972;Schäffer et al, 2014b) that the rate of Na-K exchange between alkali feldspar and an NaCl-KCl salt melt is controlled by the interdiffusion of Na and K in the alkali feldspar. The diffusion of Na into a single crystal of K-rich alkali feldspar thus produces a Na-rich surface layer, the thickness of which increases with time.…”

Section: Chemically Induced Fracturing In Alkali Feldsparmentioning

confidence: 99%

Effect of chemically induced fracturing on the ice nucleation activity of alkali feldspar

Kiselev¹,

Keinert²,

Gaedecke³

et al. 2021

Preprint

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Abstract. Feldspar is an important constituent of airborne mineral dust. Some alkali feldspars exhibit particularly high ice nucleation (IN) activity. This has been related to structural similarities of the ice (10-10) prism planes and the (100) planes of alkali feldspar. Here the effect of generating surfaces with close to (100) orientation by means of chemically induced fracturing on the IN activity of alkali feldspar was investigated experimentally. Gem quality K-rich alkali feldspar was shifted towards more Na-rich compositions by cation exchange with an NaCl-KCl salt melt at 850 °C, and a system of parallel cracks with an orientation close to (100) was induced. Droplet freezing assay experiments performed on grain mounts of the cation exchanged alkali feldspars revealed an increase of the overall density of ice nucleating active sites (INAS) with respect to the untreated feldspar. In addition, annealing at 550 °C subsequent to primary cation exchange further enhanced the INAS density and lead to IN activity at exceptionally high temperatures. Although very efficient in experiment, fracturing by cation exchange is unlikely to be of relevance in the conditioning of alkali feldspars in nature. However, parting planes with similar orientation as the chemically induced cracks may be generated in lamellar microstructures resulting from the exsolution of initially homogeneous alkali feldspar, a widespread phenomenon in natural alkali feldspar known as perthite formation. Perthitic alkali feldspars indeed show the highest IN activity. We ascribe this phenomenon to the preferential exposure of crystal surfaces oriented sub-parallel to (100).

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Section: Chemically Induced Fracturing In Alkali Feldsparmentioning

confidence: 99%

Effect of chemically induced fracturing on the ice nucleation activity of alkali feldspar

Kiselev¹,

Keinert²,

Gaedecke³

et al. 2021

Preprint

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“…1), which is a region on the isobaric phase diagram where two alkali feldspars of different composition coexist in equilibrium (Work et al, 2004;Brown and Parsons, 1984). At these conditions, phase separation of the originally compositionally homogeneous feldspar with c fsp K = 0.43 into submicron-scale lamellas of more K-rich and more Na-rich feldspars may have occurred (Petrishcheva et al, 2020) but was not observed in this study, as this would have required targeted analysis by transmission electron microscopy, which was beyond our scope. We refer to this annealing route as the closed system setting, and the sample produced is labeled FS08-64c.…”

Section: Cation Exchange and Annealing Experimentsmentioning

confidence: 99%

“…This process is controlled by the interdiffusion of Na and K on the alkali sublattice of the feldspar. According to the calibration of Na-K interdiffusion in alkali feldspar by Schäffer et al (2014a) and by Petrishcheva et al (2014Petrishcheva et al ( , 2020 in 8 d at 850 • C, the diffusion front would propagate a distance of 20 to 30 µm, depending on crystallographic direction. The compositional shift in the chemically altered surface layer produced sufficiently large tensile stress so that fracturing was induced, and a system of parallel cracks with an orientation close to the Murchison plane developed (see further down).…”

Section: Cation Exchange and Annealing Experimentsmentioning

confidence: 99%

Effect of chemically induced fracturing on the ice nucleation activity of alkali feldspar

et al. 2021

Self Cite

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Abstract. Feldspar is an important constituent of airborne mineral dust. Some alkali feldspars exhibit particularly high ice nucleation (IN) activity. This has been related to structural similarities of the ice (101‾0) prism planes and the (100) planes of alkali feldspar. Here the effect of generating feldspar surfaces with close to (100) orientation by means of chemically induced fracturing on the IN activity of alkali feldspar was investigated experimentally. To this end, gem-quality K-rich alkali feldspar was shifted towards more Na-rich compositions by cation exchange with an NaCl–KCl salt melt at 850 ∘C. By this procedure, a system of parallel cracks with an orientation close to the (100) plane of the feldspar was induced. Droplet-freezing assay experiments performed on grain mounts of the cation-exchanged alkali feldspars revealed an increase in the overall density of ice-nucleating active site (INAS) density with respect to the untreated feldspar. In addition, annealing at 550 ∘C subsequent to primary cation exchange further enhanced the INAS density and led to IN activity at exceptionally high temperatures. Although very efficient in experiment, fracturing by cation exchange with an alkali halide salt is unlikely to be of relevance in the conditioning of alkali feldspars in nature. However, parting planes with similar orientation as the chemically induced cracks may be generated in lamellar microstructures resulting from the exsolution of initially homogeneous alkali feldspar, a widespread phenomenon in natural alkali feldspar known as perthite formation. Perthitic alkali feldspars indeed show the highest IN activity. We tentatively ascribe this phenomenon to the preferential exposure of feldspar crystal surfaces oriented sub-parallel to (100).

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“…A movie file (gif file) showing the 3D rotations of the maps can be found in Supplementary Materials. Species loss is a known issue for APT analysis of covalently or ionically bonded materials, especially O loss in oxides or silicates [46][47][48][49]. A recent study on feldspars also showed a strong bias toward Ca in the resulting composition [43].…”

Section: Atom Probe Tomographymentioning

confidence: 99%

Revisiting the Bøggild Intergrowth in Iridescent Labradorite Feldspars: Ordering, Kinetics, and Phase Equilibria

Jin

Lee

2021

Minerals

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The enigmatic Bøggild intergrowth in iridescent labradorite crystals was revisited in light of recent work on the incommensurately modulated structures in the intermediated plagioclase. Five igneous samples and one metamorphic labradorite sample with various compositions and lamellar thicknesses were studied in this paper. The lamellar textures were characterized with conventional transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The compositions of individual lamellae were analyzed with high-resolution energy-dispersive X-ray spectroscopy (EDS) mapping and atom probe tomography (APT). The average structure states of the studied samples were also compared with single-crystal X-ray diffraction data (SC-XRD). The Na-rich lamellae have a composition of An44–48, and the Ca-rich lamellae range from An56 to An63. Significant differences between the lamellar compositions of different samples were observed. The compositions of the Bøggild intergrowth do not only depend on the bulk compositions, but also on the thermal history of the host rock. The implications on the subsolidus phase relationships of the plagioclase feldspar solid solution are discussed. The results cannot be explained by a regular symmetrical solvus such as the Bøggild gap, but they support an inclined two-phase region that closes at low temperature.

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Spinodal decomposition in alkali feldspar studied by atom probe tomography

Cited by 13 publications

References 49 publications

Effect of chemically induced fracturing on the ice nucleation activity of alkali feldspar

Effect of chemically induced fracturing on the ice nucleation activity of alkali feldspar

Effect of chemically induced fracturing on the ice nucleation activity of alkali feldspar

Revisiting the Bøggild Intergrowth in Iridescent Labradorite Feldspars: Ordering, Kinetics, and Phase Equilibria

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