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
What Is Spiritism? What Is Spiritism? What Is Spiritism? ("Qu'Est-ce Que le Spiritisme" in French) is a brief introduction to Spiritism written by Allan Kardec in 1859, which is about a quarter of the length of The Spirits Book. Modern editions are augmented by a brief biography of the author, written by Henri Sausse, in 1896 which is mostly focused on his role in the History of Spiritism. The book is structured as a series of conferences about Spiritism, intended to quench the public curiosity and dismiss false notions about the doctrine. It is not intended as an initiation and is not seen