Plain visible-light micrographs, effective thickness, and X-ray fluorescence images for the same area as that shown in ( a d ). The fluorescence images are in units of mass concentration (mass m -3 ). The maximum (M) and minimum (m) values for the range are given above each image and the asterisk (*) indicates a logarithmic scale. The electron shell whose vacancy is filled for fluorescence is given in parentheses next to each chemical element. Monochrome visible-light images were captured using the differential interference contrast microscope whereas color ones were observed with the digital microscope.
