Organic matter rich diatomite can be freed of its organic carbon by burning, other contaminant cannot easily be removed. Chemical composition is highly variable from outcrop to outcrop and within outcrops. Great effort is exercises to either mine only the highest quality or to chemically or physically improve the quality of kieselgur by removing oxides, carbonate, and organic matter and to improve porosity by grinding and mortaring.
Chemical industry can only use the highest grades.