The Spectrochemical Determination of Feldspars within the Field Microcline-Albite-Labradorite

W. E. Fraser and G. Downie
Dept. of Geology and Mineralogy, Marischal College, University of Aberdeen

Summary: Two spectrochemical methods of feldspar determination are described: one based on the flame spectrophotometer; the other on the quartz spectrograph. For the first method, unknown feldspars are dissolved in a mixture of hydrofluoric and perchloric acids and diluted to 1 : 104. Percentages of Or and An are determined by comparison with dissolved feldspar standards at the same dilution; percentages of Ab are estimated by difference. For the second method, unknown feldspars are burned, unadulterated, in the cathode of the spectrograph are and a visual estimation is made of the intensities of the following lines: Na5688, Na5683, Ca4455, Ca4435, Ca4425, K4047, K4044, Ca3644, K3447, Na3303, Na3302, and Ca3159. The estimated intensities are then substituted in two empirically determined functions:

(ICa4455+ICa4435+ICa4255+ICa3644+ICa3159)−43(INa5688+INa5683+INa3303+INa3302)and (3INa5688+3INa5683+2INa3303+INa3302)−43(4IK4047+3IK4044+2IK3447) .

From the algebraic values of these two functions, the compositions of the unknown feldspars, expressed as percentages of Or, Ab, and An, are read directly from a chart based on results obtained from feldspar standards of known chemical composition.

Mineralogical Magazine; March 1964 v. 33; no. 264; p. 790-798; DOI: 10.1180/minmag.1964.033.264.07
© 1964, The Mineralogical Society
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