Archaeometric application of the Raman microprobe to the non-destructive identification of two pre-Columbian ceremonial polished ‘greenstone’ axe-heads from Mesoamerica
✍ Scribed by David C. Smith; François Gendron
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 363 KB
- Volume
- 28
- Category
- Article
- ISSN
- 0377-0486
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✦ Synopsis
Two ceremonial polished "greenstoneÏ axe-heads from Mesoamerica were examined with a Raman microprobe in order to identify the mineral phases present, and hence to classify the rock type, as a feasibility test of this non-destructive method, i.e. an alternative to conventional destructive archaeometric methods such as diverse analyses made upon drilled cores, sawn slices, chipped fragments or scraped powders. Axe-head 1 from Mexico, constituted of a green rock with noticeable disseminated red or black minerals, revealed the presence of garnet, clinopyroxene and titanite with probable clinoamphibole ; this is an eclogite since the available calibrations of the chemical variation of garnet or clinopyroxene mineral solid solutions with Raman wavenumber shifts permit semiquantitative chemical analyses of these two critical minerals. Axe-head 2 from Guatemala consists of a uniform bluish green coloured mineral which is shown here to be nearly pure jadeite jade ; the rock is thus a jadeitite. Both rock types are dense, hard, aesthetic and valuable. Known geological localities for either of these rock types are rare world-wide, especially in the Americas, as their mineral assemblages with Al predominantly in octahedral coordination require unusually high pressure for their crystallization. Axe-head 1 is the Ðrst record for the pre-Columbian utilization of, and commerce in, eclogite in Mesoamerica. This feasibility study demonstrates the utility of the Raman microprobe for the physico-chemical characterization of precious archaeological artefacts in stone. It is suggested that this technique could and should become a routine approach in archaeometry for identiÐcations and provenancing.