The detection of quartz in clay minerals by differential thermal analysis

Abstract

Differential thermal analysis (DTA) has proven to be a sensitive, specific and relatively rapid technique for the detection of small amounts of free crystalline quartz in clay minerals. The method utilizes the thermal transition representing the reversible alpha—beta crystal inversion of quartz at 573°C. On heating, the latent heat of inversion gives rise to an endothermic reaction; on cooling, an exothermic transition is obtained. The mineral is first calcined at approximately 800°C for the purpose of inducing irreversible thermal transitions characteristic of that mineral and its impurities. The cooling curve then shows a flat baseline, thus improving detectability for quartz. With the use of standard prepared samples of quartz in talc, the minimum level of detection of quartz by DTA was determined to be 0.5% by weight. If sample preparation and experimental parameters are standardized, DTA provides a definitive technique for detection of quartz in clay minerals. The method has also been applied for the detection of quartz in industrial dust and in respirable particle size material such as might be taken from personnel air samplers.