Petrography

From ArchaeoWiki

Petrography (also commonly referred to as petrographic analysis) is the branch of petrology (the study of rocks and minerals—therefore an integral part of geology) that seeks to make detailed examination and description of rocks, minerals and sediments in order to draw conclusions regarding their origin and manipulation. In the late 20th and earliest 21st centuries CE, petrography has come increasingly to be regarded as having multiple archaeological applications, not least in the region of the ancient Near East and Egypt.

1 Techniques
2 Application
3 Specific Applications
4 Bibliography
5 External links

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Techniques

In research conducted by a petrographer, the mineral content and textural relationships within the chosen material are described in detail. Petrographic descriptions frequently begin with preliminary field notes at the outcrop or upon examination of an appropriate artefact, and include megascopic description of hand specimens. By far the most important tool for petrographic examination, however, remains the petrographic microscope for detailed analysis of minerals by optical mineralogy in thin section, the microtexture and structure being critical to understanding the origin of the material studied. In more advanced petrographic laboratories, electron microprobe analysis of individual grains is employed, in addition to whole rock chemical analyses by atomic absorption or X-ray fluorescence. Individual mineral grains may also be analyzed by X-ray diffraction when normal optical means are insufficient. Finally, the analysis of microscopic fluid inclusions within mineral grains with a heating stage on a petrographic microscope can provide clues as to the temperature and pressure conditions prevailing during the mineral formation.

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Application

Petrographic analysis is most commonly employed by archaeologists to identify the mineral components present in clays used to manufacture ceramic vessels, clay tablets and other pottery objects. These data can then be used to link the artefacts to geological source areas for both the clay used and the mineral and other fragments (usually called "temper" or "aplastics") often added by potters to modify the properties of the clay. This information can provide insight into the means by which potters were selecting and using local and non-local resources, as well as allowing archaeologists to determine whether pottery found in a particular location was locally produced or imported. This information in turn, combined with other pertinent evidences, can be used to build inferences regarding settlement patterns, group and individual mobility, and social contacts or trade networks. Moreover, an understanding of how certain minerals alter at specific high temperatures can allow archaeological petrographers to infer aspects of the ceramic production process itself, such as minimum and maximum temperatures reached in the original firing of the pot.

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Specific Applications

Perhaps the best known recent application of petrographic analysis has been the examination of the majority of the Amarna Tablets by Professor Yuval Goren of Tel Aviv University, who—in concert with his colleagues Israel Finkelstein and Nadav Naʾaman—has been able to produce abundant new insights into communication and geopolitical aspects of the Amarna Period in Egypt and Canaan.

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Bibliography

Goren, Yuval, Finkelstein, Israel and Naʾaman, Nadav [2002], “The Seat of Three Disputed Canaanite Rulers According to Petrographic Investigation of the Amarna Tablets”, TA 29.2 (2002), pp.221-237.
[2003], “The Expansion of the Kingdom of Amurru According to the Petrographic Examination of the Amarna Tablets”, BASOR 329 (2003), pp.3-11.
[2004], Inscribed in Clay: Provenance Study of the Amarna Tablets and Other Ancient Near Eastern Texts, Tel Aviv: Sonia and Marco Nadler Institute of Archaeology, University of Tel Aviv, 2004. ISBN 9652660205

Goren, Y., Bunimovitz, Shlomo, Finkelstein, I. and Naʾaman, N. [2003], "The Location of Alashiya: New Evidence from Petrographic Investigation of Alashiyan Tablets”, AJA 107.2 (2003), pp.233-255. html complete pdf

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