Evolution of chemically induced cracks in alkali feldspar: thermodynamic analysis

Abart, Rainer; Petrishcheva, Elena; Habler, Gerlinde; Sutter, Christoph; Fischer, Franz Dieter; Predan, Jožef; Kegl, Marko; Rammerstorfer, F.G.

doi:10.1007/s00269-022-01183-9

“…The action of tear would produce new sections, leading to potassium feldspar crystal lattices with broken bonds, dislocations, and uneven textures. Cation exchange along the newly formed crack flanks produced Na-enriched diffusion halos around the cracks, and the associated lattice contraction and tensile stress state caused continuous crack growth [ 32 ]. These features changed the XRD peaks.…”

Section: Discussionmentioning

confidence: 99%

Mechanism of Potassium Release from Feldspar by Mechanical Activation in Presence of Additives at Ordinary Temperatures

Zhang,

He,

Jia

et al. 2023

Materials

3

0

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To improve the potassium availability of feldspar at ordinary temperatures, the mechanical grinding and addition of sodium hydroxide/salts were employed to study the effects of mechanical activation and strong alkali addition on particle characteristics, water-soluble potassium, and the available potassium of feldspar. A laser particle size analyzer was utilized for the direct determination of particle size distribution (PSD) using ground samples. The Brunauer–Emmett–Teller (BET) method was employed for specific surface areas. X-ray diffraction (XRD) was employed for structural characterization, scanning electron microscopy (SEM) for morphology exploration, and energy dispersive spectroscopy (EDS) to determine the chemical composition of potassium feldspar powder. The results revealed that the mechanical activation of potassium feldspar could reduce the particle size and produce agglomerated nanoparticles in the later period. The addition of NaOH and sodium salt did not cause agglomeration, and NaOH dissolved the nanoparticles. The water-soluble potassium content of feldspar in each treatment increased during mechanical grinding, from 21.64 mg kg−1 to 1495.81 mg·kg−1, by adding NaOH 5% weight of potassium feldspar powder and to 3044.08 mg·kg−1 by adding NaOH 10% weight with effects different from those of mechanical shaking. By comparison, only 162.93 mg·kg−1 water-soluble potassium was obtained by adding NaOH 5% weight. The dissolved potassium in the former case was significantly higher than in the latter, and the addition of NaOH and sodium salts significantly enhanced the water-soluble potassium contents due to ion exchange. Furthermore, the addition of sodium hydroxide improved the water-soluble potassium due to its mechanochemical action on potassium feldspar. The mechanical energy changed the crystal structure of potassium feldspar, explaining the increase in available potassium. The addition of sodium salts did not promote change in the feldspar’s structure, thereby did not raise the available potassium content. The reason for this was related to the mechanochemical action on sodium hydroxide and feldspar, which could promote the dissolution of fine particles, thereby incrementing the available potassium.

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Thermodynamic mixing properties of disordered alkali feldspar solid-solution from Na–K partitioning and low-temperature calorimetry

Heuser,

Petrishcheva,

Ingegneri

et al. 2024

Phys Chem Minerals

1

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The equilibrium partitioning of Na and K between alkali feldspar and NaCl–KCl salt melt was determined at 800 $$^\circ$$ ∘ C, 850 $$^\circ$$ ∘ C, 900 $$^\circ$$ ∘ C, 950 $$^\circ$$ ∘ C and 1000 $$^\circ$$ ∘ C and close to ambient pressure. Four different natural gem-quality alkali feldspars with low degree of Al–Si ordering covering the range from orthoclase to high sanidine and with slightly different minor element concentrations were used as starting materials. The partitioning curves obtained for the four feldspars are indistinguishable indicating that Na–K partitioning independent of the differences of Al–Si ordering state and minor element concentrations existing amongst these feldspars. A sub-regular two parameter Margules type solution model was fitted to the partitioning data, and the excess Gibbs energy describing the thermodynamic non-ideality of the alkali feldspar solid-solution and the respective Margules parameters $$W_{\text {g}\text {K}}$$ W gK and $$W_{\text {g}\text {Na}}$$ W g including their temperature dependence expressed as $$W_g=W_h-TW_s$$ W g = W h - T W s were determined: $$\begin{aligned} W_{\text {g}\text {K}}&= 19754 \pm 3140 J\cdot \,\,{\hbox {mol}}\,\,^{-1} - T \cdot 2.33 \pm 2.67 J\cdot \,\,{\hbox {mol}}\,\,^{-1}\cdot K^{-1} \\ W_{\text {g}\text {Na}}&= 14916 \pm 4272 J\cdot \,\,{\hbox {mol}}\,\,^{-1} - T \cdot 3.55 \pm 3.64 J\cdot {\hbox {mol}}\,\,^{-1}\cdot K^{-1} \\ \end{aligned}$$ W gK = 19754 ± 3140 J · mol - 1 - T · 2.33 ± 2.67 J · mol - 1 · K - 1 W g = 14916 ± 4272 J · mol - 1 - T · 3.55 ± 3.64 J · mol - 1 · K - 1 The corresponding solvus has a critical temperature slightly above 650 $$^\circ$$ ∘ C and is well comparable with earlier direct experimental determinations of the low-sanidine-albite solvus curve. Comparison of the vibrational excess entropy determined from low-temperature heat capacity measurements with the total excess entropy derived from the temperature dependence of the excess Gibbs energy yields a negative configurational contribution to the excess entropy pointing towards short-range Na–K ordering on the alkali site.

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Magmatic processes forming replacement textures with fluorite alignments in feldspars in an evolved trachyte from Oki‐Dogo Island, Sea of Japan

Nakano,

Makino

2024

Island Arc

1

0

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Internal microtextures of ternary alkali feldspars in sanidine trachyte from Oki‐Dogo Island were examined using an electron microprobe analyzer, a scanning electron microscope, a transmission electron microscope and cathodoluminescence instruments, to develop the understanding of volcanic processes of alkaline magmas related to feldspar crystallization. The examined trachyte is an evolved rock of the Oki‐Dogo Pliocene trachyte group. Its phenocryst feldspars are commonly associated with lamellar‐wavy‐domain textures with scales approximately from 100 nm up to several hundreds of μm that show complex and gradual variations in composition: however, anti‐rapakivi zoning textures common in other Oki‐Dogo alkaline rocks are almost completely absent in the trachyte. These textures are produced by extensive magmatic ion‐exchange replacement reactions progressively advanced in the evolved magma. Characteristic braided fluorite alignments are developed consistently with lamellar‐wavy‐domain textures in phenocryst feldspars, and similar braided alignments are also present in groundmass feldspars with complicated microtextures. Most of fluorite grains are <100 nm in diameter, and the patterns of braided fluorite alignments vary greatly in individual feldspars. The whole occurrence of the feldspar microtextures represents an extreme example of diffusion‐controlled replacement reactions, progressively advanced in the dry (relatively anhydrous) trachyte magma. The genetic processes forming fluorite alignments in feldspars are related to magma compositions, especially F and P contents, and the crystallization of F‐bearing minerals, especially of fluorapatite.

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Evolution of chemically induced cracks in alkali feldspar: thermodynamic analysis

Cited by 4 publications

References 51 publications

Mechanism of Potassium Release from Feldspar by Mechanical Activation in Presence of Additives at Ordinary Temperatures

Mechanism of Potassium Release from Feldspar by Mechanical Activation in Presence of Additives at Ordinary Temperatures

Thermodynamic mixing properties of disordered alkali feldspar solid-solution from Na–K partitioning and low-temperature calorimetry

Magmatic processes forming replacement textures with fluorite alignments in feldspars in an evolved trachyte from Oki‐Dogo Island, Sea of Japan

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