Sodium-potassium interdiffusion in potassium-rich alkali feldspar II

Author(s)
Anne-Kathrin Schäffer, Elena Petrishcheva, Gerlinde Habler, Rainer Abart, Dieter Rhede, Gerald Giester
Abstract

Na-K interdiffusion in disordered potassium-rich alkali feldspar was studied experimentally using cation exchange between gem quality sanidine from the Eifel and alkali-halide melt at temperatures of 800°C to 1000°C and at close to ambient pressure. Sodium-potassium interdiffusion coefficient D

NaK was determined for potassium mole fractions in the range 0.65 ≤ X

Or ≤ 0.99. At 0.65 ≤ X

Or ≤ 0.95 the sodium-potassium interdiffusion coefficient is largely independent of composition. At X

Or ≥ 0.95, it rises sharply with increasing potassium mole fraction. Diffusion perpendicular to (001) is about one order of magnitude faster and less strongly temperature dependent than perpendicular to (010). The parameters of the Arrhenius equation describing the temperature dependence of the sodium-potassium interdiffusion coefficient D

NaK = D

0Exp (-E

A/RT) were estimated as D

0

⊥(001)(0.92) = 5.18 · 10

-8 m

2/s, E

A

⊥(001)(0.92) = 179kJ/mole D

0

⊥(001)(0.98) = 1.82 · 10

-7 m

2/s, E

A

⊥(001)(0.98) = 182kJ/mole D

0

⊥(010)(0.92) = 5.81 · 10

-5 m

2/s, E

A

⊥(010)(0.92) = 272kJ/mole D

0

⊥(010)(0.98) = 1.34 · 10

-4 m

2/s, E

A

⊥(010)(0.98) = 269kJ/mole The results of our direct determinations are compared with theoretical calculations using the corresponding sodium- and potassium tracer-diffusion coefficients, and the processes underlying the observed composition- and temperature dependence of sodium-potassium interdiffusion are discussed.

Organisation(s)
Department of Lithospheric Research, Department of Mineralogy and Crystallography
External organisation(s)
Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum
Journal
American Journal of Science: an international earth science journal
Volume
314
Pages
1300-1318
No. of pages
19
ISSN
0002-9599
DOI
https://doi.org/10.2475/09.2014.03
Publication date
11-2014
Peer reviewed
Yes
Austrian Fields of Science 2012
105116 Mineralogy, 105113 Crystallography, 105120 Petrology
Keywords
ASJC Scopus subject areas
General Earth and Planetary Sciences
Portal url
https://ucrisportal.univie.ac.at/en/publications/7a49776e-79d1-440d-83cd-1adab6c1de02