With the very large information depth available in micro-beam XRF it is possible to generate 2-dimensional maps of the elemental distribution over large spherical fly-ash particles with a resolution down to about 1 µm. These particles possess a large degree of spherical symmetry due to the process of their formation. By applying special reconstruction algorithms the symmetric part of the elemental distribution can be reconstructed from the 2-dimensional projection maps and subtracted from the original map. The result shows that such a fly-ash particle can be split into a radial symmetric part containing non-volatile carbonaceous compounds and an asymmetric part representing precipitates or sub-particles formed within the fly-ash particle. The symmetric part showed a distinct feature of an outer and an inner shell. From the asymmetric part the interior of the fly-ash particle can be studied without interference of the inner and outer shells.