Petrography lower if wholly or partly vitreous. The specific gravity of the more common rocks range from about 2.5 to 3.2. Archaeologists use petrography to identify mineral components in pottery. This information ties the artifacts to geological areas where the raw materials for the pottery were obtained. In addition to clay, potters often used rock fragments, usually called "temper" or "aplastics", to modify the clay's properties. The geological information obtained from the pottery components provides insight into how potters selected and used local and non-local resources. Archaeologists are able to determine whether pottery found in a particular location was locally produced
Ceramic petrography in the prehistoric Aegean. In the USA the approach is less popular, though important contributions have been made in the area of quantitative petrography. Other attempts to extend ceramic petrography include the use of automated image analysis, the palaeontological analysis of microscopic fossils within ceramic thin sections and the combined statistical classification of petrographic and chemical data from artefacts. Thin section archaeological petrography can be applied to a range of other artefact types in addition to ceramics; these include plaster, mortar, mudbricks and lithic implements. Academic papers on ceramic petrography are often published in journals such as Archaeometry, Journal of