DETERMINATION OF QUARTZ IN KAOLINS BY X-RAY-POWDER DIFFRACTOMETRY

Depending upon their origin, naturally occurring kaolins contain various accessory minerals including micas, feldspars and quartz. These minerals may be partially removed, but rarely eliminated, by refining. When determining quartz by x-ray diffractometry, serious problems are encountered even with refined kaolins due to overlapping peaks from micas, feldspars and kaolinite itself. This paper discusses the peak overlap and other problems and describes how optimisation of sample preparation and diffractometer parameters, together with the use of profile fitting techniques permits the determination of crystalline quartz in bulk samples to +/- 0.015 wt.% (1sigma absolute) at the 0.1 wt.% level. A detailed examination of the errors involved in the analysis shows that counting and particle statistics are the most important error sources. For the samples examined in this study, counting statistics is the major contributor to the observed 15% relative error. Preliminary results on the use of a laboratory air classifier to generate ''large'' respirable dust samples from bulk powders for quartz analysis are given.