The goal of the data base is to characterize specimen from known prehistoric quarry sites on the basis of: 1) Macroscopic features, 2) petrographic characteristics, and 3) geochemical composition. The "Test Data-Base" is our first attempt to achieve these goals, and should be considered a work in progress. At present, the initial effort is directed toward the characterization of volcanic felsite. Some of the longer term goals include: 1) refinement of the data base input information, and development of interactive search capabilities, 2) expansion of the data base to include additional well documented samples of felsite, and other archaeological materials, such as chert, argillite, soapstone, other kinds of volcanic rocks, etc., and 3) development of a similar, linked data base for archaeological artifacts and debitage.
Follow this link to view the Proposed Database
Template
and a sample of the template based on the Lynn-Mattapan
Rhyolites.
Follow this link to view thin-sections and hand-samples mentioned in the text.
See also: Thin sections and descriptions of some New
England Rhyolites and other lithics, prepared by Barbara Calogero.
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Generalized geologic map of southeastern New England showing distribution of volcanic rocks (after Hermes and Murray, 1990; Hermes and Ritchie, 1997). Locations of prehistoric archaeological quarry sites for most samples used in the "Test Database" are shown by yellow circles: WH = Wampatuck Hill, HR = Hale Reservation, CH = Clarendon Hill, MS = Mattapan Square, MN = Marblehead Neck, WM = Wamsutta rhyolite. |
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Prehistoric quarry-site samples of felsite from areas surrounding the
Boston basin region of eastern Massachussets (after Hermes and Ritchie,
1997). Samples are plotted on the classification diagram for volcanic rocks
(after Le Bas and others, 1986), which is based on SiO2 vs.
Na2O + K2O. This diagram is especially useful for
the classification of fine-grained volcanic rocks if major element chemistry
is available, and if the rocks have not undergone extensive alteration
or metamorphism so as to disturb the original alkali element content.
(Click on the image for a more detailed view.) |
POTENTIAL TRACE ELEMENT DISCRIMINATION DIAGRAMS
The following trace element discriminant diagrams have been useful in distinguishing felsite sources in southeastern Massachusetts (after Hermes and Ritchie, 1997). Plotted points represent known prehistoric quarried material that was a source for known archaeological artifacts and debitage. Note that the plots are log-log plots. The polygonal fields are based on bedrock geologic studies of Hermes and Murray (1990) and Thompson and Hermes (1990). The diagrams, either individually or collectively, discriminate samples from the major volcanic complexes in southeastern New England. Discrimination of specimen from separate sub-units of a complex (e.g., the Lynn, Twin Pine, and High Rock units of the Lynn-Mattapan complex) are more problematic and may exhibit some overlap.
Click on the following images to load a more detailed picture.
Zr vs. Nb
Rb/Sr vs. Zr/Ba
Zr +Ce + Y vs. Rb/Ba
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