Study of Archaeological Stone

The Components of Materials. The composition of mosf materials -whefher of natural origin, such as minerals, rocks, wood, and skin, or made by humans, as for example, pottery, glass and alloys - includes several kinds of components major, minor, and trace elements (see Textbox 8). 

COMPOSITION OF MATERIALS MAJOR, MINOR, AND TRACE COMPONENTS 

Substances prepared under carefully controlled conditions and using very pure chemicals, in a modern laboratory, for example, contain only the basic component elements, those that determine the actual composition and nature of the substances. Natural substances, whether of mineral or biological origin, and also most synthetic (human-made) substances contain, in addition to their main components, impurities foreign to their basic composition. Most impurities usually enter substances such as minerals, for example, in relatively small amounts, when the substances are created. Others, such as those in some rocks and the wood of trees, do so in the course of their existence. Once within a substance, impurities become an integral part of the host substance and impair the purity of the substance. Although they alter the actual composition of substances, impurities do not affect their basic properties. 

three types of components can be distinguished in most substances, whether of natural origin or made by humans major, minor, and trace components (see Table 8). The major components, also known as the main or matrix components, are those that determine the chemical nature and properties of a substance. The major components occur in the substance in high concentration, generally exceeding 1 % of the total weight. In minerals and biological substances, for example, the major components are those that appear in the chemical formula that expresses their composition. 

In practically all natural and in most synthetic substances there are, mixed with the major components, impurities in minor and trace amounts. Minor components occur in concentrations below 1 % and down to about 0.1% of the total weight of a sample of the substance. Many additional impurities, usually referred to as trace components or trace elements, occur in host substances at extremely low concentration, generally below 0.1% their concentration is generally expressed either as parts per million (ppm) or parts per billion (ppb) (1 ppm is equivalent to a one gram in one ton 1 ppb, to one gram in one million tons). Minor and trace impurities do not alter the basic composition, nor do they affect most of the properties of substances, but they may change, even drastically, some of their physical properties. Trace impurities in otherwise colorless minerals, for example, often make the minerals highly colored. 

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Bones and teeth, however, are primary archaeological materials and are common to many archaeological sites. Bones bearing cut marks from stone tools are a clear proxy for human occupation of a site, and in the study of human evolution, hominid remains provide the primary archive material. Hence, many attempts have been made to directly date bones and teeth using the U-series method. Unlike calcite, however, bones and teeth are open systems. Living bone, for example, contains a few parts per billion (ppb) of Uranium, but archaeological bone may contain 1-100 parts per million (ppm) of Uranium, taken up from the burial environment. Implicit in the calculation of a date from °Th/U or Pa/ U is a model for this Uranium uptake, and the reliability of a U-series date is dependent on the validity of this uptake model. 

Williams-Thorpe, O., Potts, P. J., and Webb, P. C. (1999). Field-portable non-destructive analysis of lithic archaeological samples by X-ray fluorescence instrumentation using a mercury iodide detector Comparison with wavelength-dispersive XRF and a case study in British stone axe provenancing. Journal of Archaeological Science 26 215-237. 

This chapter is an overview of the wide variety of archaeological studies conducted by chemists. From the earliest stone artifacts to the artistic manuscripts and textiles of the more recent past, the studies presented in this volume show the wide range of materials that have been studied by chemical techniques. The field keeps expanding as chemists help provide information valuable in the interpretation of archaeological sites and artifacts. Besides helping to detect fraudulent artifacts and artistic objects in museum collections, chemists have studied the physicochemical deterioration processes that destroy the monuments and objects of the past. Thus, the role of chemists is more than just discovery of the past it includes investigation that may help preserve the artifacts for future generations to enjoy and study. 

Research in the laboratory usually involves the study of the composition and source of different kinds of materials to answer archaeological questions about past human behavior. The lab methods involve the trace element and isotopic analyses of bones, stone, ceramics, and sediments and have expanded to include organic residues, lithics, pigments, and other materials. Research questions include past diet, human migration, raw material sources, interaction and trade, and the identification of activity areas on prehistoric sites. 

Of great use in such investigations are artifacts or materials that come from a known location. It is in this area that archaeological chemistry has made an enormous contribution. There are many cases of such movement in exotic materials, often in the form of rare stones or minerals. There were no natural sources of turquoise in ancient Mexico, for example, but tins beautiful blue-green stone was imported from the present state of New Mexico and used in the costumes and jeweliy of the elite in Aztec Mexico.. Archaeological chemistry had documented the sources of turquoise in the southwestern and found objects from Mexico that clearly came from those quarries. This example is discussed in more detail in Chap. 8, Case Studies. 

Case studies of functional investigations in archaeological chemistry described here include two of the most common classes of archaeological remains - the microscopic analysis of early stone tools and the application of organic chemistry to determine what pottery was used for by hunter-gatherers in prehistoric Denmark. There are many other studies, not discussed here, regarding the use of prehistoric artifacts and structures to be found in the archaeological literature. 

Our knowledge of prehistoric diets has been derived mainly from archaeological studies of charred food remains and dried fecal material found in caves and at the sites of ancient camps. Also, there have been many studies of the aborigines who are still engaged in stone age practices in such parts of the world as Africa, Australia, New Guinea, and the Philippines. 

Written records provide a valuable glimpse into the thoughts and behavior of ancient peoples. But these records are not complete and omit important information (important, that is, to historians). Scientists studying the past have had to turn to other sources such as analyzing artifacts. Archaeological finds are a rich source of information, if that information can be unlocked. The need is to find a Rosetta stone for other types of artifacts—a method of gleaning all the information that is available. 

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