Mapping of weathered sedimentary rock for iron distribution

Analytical Challenge
Geologists are keenly interested in cause and effect with respect to the ancient climatic records that are rocks. Insight into compositional changes due to weather conditions of long ago periods in the Earth's history can be garnered through the application of modern analytical tools such as WDXRF with mapping capabilities. Here is an example of what compositional changes might be seen in a weathered rock specimen's exposed surface and, say, its interior.

Analytical Approach
The 4 kW Rigaku ZSX Primus X-ray spectrometer was used to collect intensity data thru small spot analysis/mapping to determine the cause of discoloration of a partially discolored sedimentary rock. Using the magnified CCD camera image of the rock specimen, a region of interest was defined for point analysis/mapping for Fe.

The CCD camera is self-contained within the analytical chamber and the and the individual analysis spots are moved into measuring position with a sample stage driving mechanism. The mapping analysis can be conducted with an analytical diameter as small as 0.5 mm.

Measurement result
Figure 1 shows a magnified picture of the sample surface along with the qualitative analysis result from a 1 mm dia. measuring area. From the qualitative analysis chart we can see that a greater quantity of iron exists in the dark-colored region of the rock which corresponds to the blue iron peak, regarded as the discolored region, than in a lighter-colored region of the specimen, considered to be the original color, and this corresponds to the red iron peak.

sample surface along with the qualitative analysis result
Figure 1: CCD magnified picture (left) and qualitative chart (right)

Figure 2 shows the result of mapping analysis of this iron over a 0.5 mm dia. analysis area. It is apparent that a large quantity of Fe is contained in the discolored portion.

result of mapping analysis
Figure 2: 2D (left) and 3D (right) results of mapping analysis of Fe-Kα

The Rigaku Primus series continues to prove its utility in varied geological challenges, through its unique elemental mapping capabilities.