MAJOR-ELEMENT ANALYSIS OF SELECTED ROCK AND VOLCANIC ASH SAMPLES IN THE UNZEN AREA, JAPAN, BY X-RAY-FLUORESCENCE SPECTROSCOPY

Determination of major elements in natural solid samples by X-ray fluo rescence spectroscopy (XRF) with a fusion disc technique is described. Data obtained by the present XRF analytical system were found to have satisfactorily high reliability. Five rock samples and a volcanic ash sample with varying ages ranging from the present to 180 000 years, d erived by the current and past volcanic activities in the Unzen area, Nagasaki, Japan were analyzed for their major elements' compositions u sing the above mentioned system. The chemical composition of the magma under this area has changed very little at least over the last 180 00 0 years.