Luminescence Properties of Chert and some Archaeological Applications

We have examined the cathodoluminescence (CL) and induced thermoluminescence (TL) properties of chert collected from the Ozark Mountains area of the central United States. The cherts showed predominately orange CL with occasional blue CL. X-ray diffraction indicates that the amount of orange CL correlates closely with the abundance of carbonates within the chert. Previous studies have shown that macroquartz characteristically gives off a weak and transient blue CL. Thermoluminescence studies concentrated on the shape of the radiation induced TL glow curve. The results seem to indicate all of the cherts sampled fall into one of four glow curve categories. The TL categories correspond to quartz crystallinity as measured by X-ray diffraction, which is probably a reflection of quartz grain size. Application of these techniques is somewhat new to chert studies, but may provide a useful criterion in establishing the number of chert varieties or sourcing chert provenience locations for artefacts collected from archaeological sites. Calcite and dolomite are expected to leach from chert surfaces upon exposure to weathering agents, thus making CL a helpful tool for the detection of fake stone artefacts with fresh fracture surfaces. Quartz crystallinity is an important factor in determining chert cleavage characteristics and TL appears to be a useful measure of this property.