標準試料の測定に基づく徳島大学EDSにおける珪酸塩鉱物化学組成データの補正

In order to obtain as closely accurate stoichiometry by EDS at Tokushima University (Hitachi SU3500 with EDAX Elements) as by WDS, we carried out EDS analyses for chemical composition of 10 standard minerals (albite, almandine, biotite, bustamite, diopside, jadeite, kaersutite, olivine, plagioclase An65 and sanidine), compared the measured values with their recommended values and then, determined correction factors for 9 major elements in silicate minerals. Linear regressions were adopted for 6 elements, Ca, Al, Mg, Ti, Mn and Fe, and proportional correction factors ranging from 0.9083 for Ca to 1.0574 for Mg were determined for each element. For Na and K quadratic approximations were adopted and yield 1st and 2nd order correction factors for each. For Si, due to the output style of the EDS data with the cation total normalized to 100%, uses of a common (average) correction factor for all silicate minerals are improper because of the relative over- or under-estimate of Si against the other combined elements that depends on mineral species. The correction factor for Si, therefore, is not fixed and is determined manually for each mineral specie so as to achieve its stoichiometric total cation number. It is confirmed that use of the above-mentioned correction factors improves stoichiometries for all the silicate minerals examined in this study. Total of 3 times of determinations for correction factors carried out over a period of about 6 months, during which the filament of the electron-gun was once broken and replaced to new one, suggest that errors in stoichiometry due to different aging conditions of the filament are negligible and the first set of correction factors determined on June 29th 2021 can be used semi-permanently.