| dc.description.abstract | Powder XRD is a popular method for mineral quantification, but it often
remains semi-quantitative due to difficulties such as preferred orientation in
clays and feldspars. Preferred orientation effects are minimised when a full
pattern summation quantification method is used. The quantitative powder
XRD workflow developed here is centred around such a full pattern summation
method: the R application powdR (Butler 2020). PowdR requires a reference
library consisting of reference patterns of all to-quantify minerals. A reference
library consisting of quartz, calcite, Ca-montmorillonite, labradorite, and
microcline was developed here, and used to optimize the workflow. This
optimized workflow consists of: 1) homogenising the samples in a McCrone
mill; 2) scaling the reference patterns; 3) keeping the difference in intensity
magnitude between reference patterns and sample pattern at a minimum; 4)
using peak height and averaging multiple peak pairs to obtain the reference
intensity ratio (RIR); 5) using manual instead of automatic full pattern
summation, and an internal instead of an external standard, whenever possible;
6) using your own laboratory-specific reference library instead of an external
one. The success of the peak-height approach is inconsistent with previous
research—which has suggested a peak area-based RIR approach—and the
cause of this success is unknown. When these recommendations are followed,
quantification results with a relative bias of ≤10% can be obtained. When an
external library is used instead, relative biases of ≥50% are reported. These
large errors result in incorrect interpretations of paleoenvironment,
paleoclimate, and diagenetic degree. | |
