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
Institute for the Study of Human Knowledge web site for a project entitled "The Human Journey". It aims to "follow humanity from our origins in Eastern Africa and the Middle East to the present day, with an eye to what comes next." Institute for the Study of Human Knowledge The Institute for the Study of Human Knowledge (ISHK) is a non-profit educational charity and publisher established in 1969 by the noted and award-winning psychologist and writer Robert E. Ornstein and based in Los Altos, California, in the USA. Its watchword is "public education: health and human nature information." Robert Ornstein, psychologist, writer and professor at Stanford University,