Results of an inter-laboratory comparison of methods for quantitative clay analysis

Abstract

In a comparison of analytical methods in clay mineralogy, two clay samples (from Hennersdorf and Freydegg) of different clay composition were analyzed by 19 laboratories mainly by XRD. Participants used different methods of pre-treatment, preparation, analysis and evaluation. In spite of the diversity of analytical methods applied, reasonable conformity in quantitative results was obtained for the associated minerals (quartz, calcite and dolomite). On the other hand, qualitative identification of the clay minerals showed considerably stronger divergencies, causing a stronger deviation of quantitative data; analysis of the Freydegg sample proved to have been particularly difficult. The evaluation methods of the different participants were examined to determine whether similar methods provided results that could be more easily compared. In addition, the authors calculated the clay mineral composition according to three different recognized methods, using the same diffractograms and same preparation and measuring conditions. In spite of this, different results were obtained. In the next phase of the programme, an inter-laboratory comparison of methods will be achieved under exactly defined conditions of preparation and analysis.