Studies in diffusion—III. Oxygen in feldspars: an ion microprobe determination

Self-diffusion of oxygen in adularia, anorthite, albite, oligoclase and labradorite has been measured by isotope exchange of oxygen between natural feldspars and hydrothermal water enriched in ¹⁸O. The analysis consisted of measuring the ¹⁸O/¹⁶O gradient inward from the feldspar surface using an ion microprobe, and fitting a solution of the diffusion equation to the data. Depth of the sputtered hole was measured with an optical interferometer. Linear Arrhenius plots were obtained:

	$\text{d}{}_0\text{(}\text{cm}{}^2\text{/sec}\text{)}$	$\text{Q (}\text{kcal/g-atom O}\text{)}$	$\text{T(°C)}$
Adularia (Or98)	$\text{4.51 × 10}{}^{\mathrm{?8}}$	25.6	350–700
Albite (Ab97, Ab99)	$\text{2.31 × 10}{}^{\mathrm{?9}}$	21.3	350–800
Anorthite (An96)	$\text{1.39 × 10}{}^{\mathrm{?7}}$	26.2	350–800
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