The crystal chemistry of silica-rich, alkali-deficient nepheline

Dollase, W. A.; Thomas, Warren M.

doi:10.1007/bf00373415

Cited by 68 publications

(74 citation statements)

References 26 publications

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“…Several earlier results suggest indeed that the nepheline-kalsilite framework is able to undergo such ion-exchange reactions (Dollase and Peacor 1971;Dollase and Thomas 1978;Dollase and Freeborn 1977;Henderson and Roux 1977), but these results were restricted to the system Na~K, and reconstruction could not clearly be excluded.…”

Section: Introductionmentioning

confidence: 62%

Ion exchange between tectosilicates with the nepheline-kalsilite framework and molten MNO3 or MO (M = Li, Na, K, Ag)

Sobrados

Gregorkiewitz

1993

Phys Chem Minerals

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Abstract. Natural nepheline, a synthetic Na-rich nepheline, and synthetic kalsilite were ion exchanged in molten MNO3 or MC1 (M=Li, Na, K, Ag) at 220-800 ~ C. Crystalline products were characterized by wet chemical and electron microprobe analysis, single crystal and powder X-ray diffraction, and transmission electron microscopy and diffraction. Two new compounds were obtained: Li-exchanged nepheline with a formula near (Li,Ko.3,D)Li~[A13(A1,Si)Si~O16] and a monoclinic unit cell with a=951.0(6) b=976.1(6) c=822.9(5) pm 7= 119.15 ~ and Ag-exchanged nepheline with a formula near (K,Na, D)Ag3[At3(A1,Si)Si40~6] and a hexagonal unit cell with a = 1007.4(8) c = 838.2(1.0) pm. Both compounds apparently retain the framework topology of the starting material. Ion exchange isotherms and structural data show that immiscibility between the end members is a general feature in the systems Na-Li, Na-Ag, and Na-K. For the system Na-K, a stepwise exchange is observed with (K,D)Na3[A13(AI,Si)Si40~6] as an intermediate composition which has the nepheline structure and is miscible with the sodian end member (Na,D)Na3[A13-(A1,Si)Si40~6], but not with the potassian end member (K,D)4[A13(A1,Si)Si4Oa6] which shows the kalsilite structure; there was no indication for the formation of trior tetrakalsilite (K/(K + Na) ~ 0.7) at the temperatures studied (350 and 800 ~ C). The exact amount of vacancies [] on the alkali site depends upon the starting material and was found to be conserved during exchange, with ca 0-0.2 and 0.3-0.4 vacancies per 16 oxygen atoms for the synthetic and natural precursors, respectively. Thermodynamic interpretation of the Na-K exchange isotherms shows, as one important result, that the sodian end member is unstable with respect to the intermediate at K/(K +Na)~ 0.25 by an amount of ca 45 kJ/mol Na in the large cavity at 800 ~ C (52 kJ/mol at 350 ~ C).

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Section: Introductionmentioning

confidence: 62%

Ion exchange between tectosilicates with the nepheline-kalsilite framework and molten MNO3 or MO (M = Li, Na, K, Ag)

Sobrados

Gregorkiewitz

1993

Phys Chem Minerals

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“…The first is formation of vacancy in the A position by the K + + Al 3+ ↔ ☐ + Si 4+ substitution, and the other is substitution of Na + for K + in the A position (Dollase and Thomas, 1978). These mechanisms reasonably explain the reason of some depletion of K and enrichment of Na in natural nephelines.…”

Section: Discussionmentioning

confidence: 80%

Crystal chemistry of K-rich nepheline in nephelinite from Hamada, Shimane Prefecture, Japan

Hamada

Akasaka²,

Ohfuji

2018

MinMag

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Running title: CRYSTAL CHEMISTRY OF K-RICH NEPHELINE FROM JAPANKEYWORDS: K-rich nepheline, X-ray structural analysis, twinning by merohedry. ABSTRACTK-rich nepheline with a structural formula of A 2 B 6 T1 4 T2 4 T3 4 T4 4 O 32 (Z = 1) within melilite-olivine nephelinite from Hamada, Shimane Prefecture, Japan, was investigated to clarify its crystal structure and to determine cation distributions in the A and B structural positions of structural channels and tetrahedral In the structural refinement, the R1 factor was reduced to 3.71 % by taking twinning by merohedry into the refinement. The refinement accounted for 77.7 % of the absolute polyhedra. The average T-O distances indicate that the T1 and T4 sites are essentially filled with Al, whereas the T2 and T3 are filled with Si. Despite the deviation of the O1 oxygen from the triad axis and the combination of K + ions and vacancies in the hexagonal channels, incommensurate structure was not observed in the X-ray diffraction data or in observation using electron diffraction technique.

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“…It locally replaces melilite. However, it is missing or very rare in scoria from Dollase & Thomas (1978). Tie-lines illustrate limits of nepheline solid solution at the shown temperatures and approximate limit at 1068 °C and 10 MPa (modified after Hamilton 1961 andBlancher et al 2010).…”

Section: G G G G Geol Eol Eolmentioning

confidence: 99%

“…Projection onto the Ne-Ks-Qz plane shown in Fig. 5 demonstrates that nephelines are mostly Ne-depleted with a considerable number of data plotting away from the "Barth join" representing natural nephelines (Dollase & Thomas 1978). The temperatures of nepheline crystallization concentrated mostly between 500 and 700 °C were estimated from the isotherms defined in Hamilton (1961).…”

Section: G G G G Geol Eol Eolmentioning

confidence: 99%

Upper Cretaceous to Pleistocene melilitic volcanic rocks of the Bohemian Massif: petrology and mineral chemistry

Skála¹,

Ulrych²,

Ackerman³

et al. 2015

Geologica Carpathica

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ratios (0.7033-0.7049) point to an additional late-to post-magmatic hydrothermal contribution. Major rock-forming minerals include forsterite, diopside, melilite, nepheline, sodalite group minerals, phlogopite, Cr-and Ti-bearing spinels. Crystallization pressures and temperatures of clinopyroxene vary widely between ~1 to 2 GPa and between 1000 to 1200 °C, respectively. Nepheline crystallized at about 500 to 770 °C. Geochemical and isotopic similarities of these rocks occurring from the Upper Cretaceous to Pleistocene suggest that they had similar mantle sources and similar processes of magma development by partial melting of a heterogeneous carbonatized mantle source.

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The crystal chemistry of silica-rich, alkali-deficient nepheline

Cited by 68 publications

References 26 publications

Ion exchange between tectosilicates with the nepheline-kalsilite framework and molten MNO3 or MO (M = Li, Na, K, Ag)

Ion exchange between tectosilicates with the nepheline-kalsilite framework and molten MNO3 or MO (M = Li, Na, K, Ag)

Crystal chemistry of K-rich nepheline in nephelinite from Hamada, Shimane Prefecture, Japan

Upper Cretaceous to Pleistocene melilitic volcanic rocks of the Bohemian Massif: petrology and mineral chemistry

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