Quantitative distribution of the alpha particle activity by nuclear emulsion techniques is applied to very fine-grained rocks. The specimens used are felsite from Loch Ba (Scotland), trachyte from Mhoire Choire (Scotland), oligoclase andesite and trachytes from Hawaii, and two basalts from Greenland. The distribution of radioactivity was found to be similar to that of other igneous rocks. More than 50 percent of the feldspar activity originates from inclusions in the feldspar. Total radioactivity showed an increase with silica and potassium content but not with the sodium content.

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