THE EFFECT OF GRINDING DURING SAMPLE PREPARATION ON THE XRF ANALYSIS OF A BASALTIC ROCK

The powders produced by different grinding conditions of five fragment s of a basaltic sample are sieved and analysed by XRF techniques. The analytical data obtained are examined with the aid of statistics, in o rder to ascertain the actual influence of powder grain size on the acc uracy of XRF analyses and to evaluate the representativeness of the an alyses carried out at Istituto Internazionale di Vulcanologia. Analyti cal results show some relationship between powder granulometry and oxi de concentrations. This effect, however does not seem attributable to powder grain size, but to mineral fractionation phenomena. Thus we sug gest both avoiding the use of a sieved powder portion and extending th e grinding time during the sample preparation stages for XRF analyses. These procedures, infact, might produce mineral fractionation rather than improvement of analytical quality.