Twenty-eight alkali feldspar perthites were analyzed for Rb content by X-ray emission spectrography, and the microcline/plagioclase ratios determined by X-ray diffraction. Pink perthites range from 78-82 weight % microcline and contain up to 0.31 weight % Rb. White perthites range from 73-94 weight % microcline and contain up to 0.18 weight % Rb. Green perthites show the greatest range in microcline content, from 70-100 weight %, and show a systematic relationship among color intensity, microcline percentage, and Rb content. Rb content of green microcline ranges from 0.06 - 1.00 weight % and is highest in dark green, microcline-rich samples.

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