Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

As has been stated e.g. in Meisel et al. (2022) that the mineralogical composition of a certain sample
does have an influence on the analytical geochemical results obtained. Prior to the start of the analytical
geochemical studies, an approximate idea of the mineralogical composition of the sample to be
analyzed should be available. This helps to select the digestion method and the methods to be used
(matrix effect).
We chose 14 samples from different GeoPT rounds representing a wide spectrum of rock composition
for a detailed quantitative X-ray diffraction (XRD) study.
Based on the determined quantitative mineralogical composition, an estimation of the chemical
composition can be made. This is achieved by a back calculation using the mineral chemistry of the
identified mineral phases. The Profex/BGMN software package (Doebelin & Kleeberg, 2015)
automatically calculates these values. These data can be directly compared with the results of a GeoPT
round robin.
It must be taken into account that the sample preparation for a GeoPT round robin is not ideal for
quantitative XRD investigations and artifacts must be expected. XRD slightly underestimates e.g.
SiO2-values (Fig. 1). This is mainly due to an overgrinding effect, where quartz forms an
“amorphization” layer at the surface (O’Connor & Chang, 1986).