A silicate mineral which is weighing 0.4700 grams gives an insoluble residue containing both Fe2O3 and SiO2 (159.7 g/mol) weighing the 0.2720 grams. Analysis of the residue shows it to contain 15.60% iron (Fe, 55.85 g/mol). Determine the percentage of SiO2 (60.09 g/mol) present in the original sample.