Examination of petrological thin-sections is an established method for assessing the mineralogical and textural properties of rock and stone implements (Fenton and Travis 1988; Cooney and Mandal 1998; Kerr 1942; Deer et al. 1992). These properties provide a petrographic fingerprint that assists with classification of rock and the grouping together of samples with similar features. In this way the Implement Petrology Group (IPG) has recognised thirty-four petrographically different groups of stone axes (Clough and Cummins 1988). In addition, by matching axe thin-sections with ones taken from rock exposures it is possible to provenance axes to exposures, a practice which is a founding tenet behind the formation of the IPG (Keiller et al. 1941).
Petrographic analysis of axe thin-sections has some limitations. Rocks from different geographical locations can have similar petrography, so petrological microscopy alone may not be able to distinguish between them. This is especially pertinent to greenstones found in Devon and Cornwall: they often share primary mineralogical characteristics, and having been partially recrystallised through low-grade metamorphic events, samples from geographically separate exposures can be difficult to tell apart (Keiller et al. 1941). Petrological variability of individual greenstone exposures means that two greenstone samples may have come from two locales metres apart on the same exposure, or from two different exposures that are many kilometres apart.
The first recorded provenancing of stone implement to exposure was achieved in 1919 (Warren 1919). In 1948 Clare Fell (Bunch and Fell 1949) identified the remains of a Neolithic 'working floor in Langdale', leading to the recognition of deliberate and concentrated manufacturing sites for Group VI axes. Once identified, more axe factories have been recognised and raised the expectation that a Group I axe factory existed and awaited discovery. Keiller et al. (1941) provenanced Group I to the Mounts Bay area of Cornwall through petrographic similarity between implements and rock from unnamed exposures between Penzance and Mousehole, heightening expectation that a Neolithic Cornish greenstone axe factory would be discovered.
This article reports on the re-examination of 149 thin-sections assigned to Group I, Ia, and III implements, carried out as part of a larger piece of research aimed at provenancing Group I implements, and which provided the basis for further non-destructive analysis of greenstone implements with the aim of locating the source exposure(s) for IPG Group I, Ia and II axes (Markham 2000).
A monocular petrological microscope was used to re-examine all thin-sections over a relatively short period of time, with a quantitative process used to substantiate the visual, qualitative, observations, leading to the ability to quantify and thus analyse the thin-sections.
Quantitative scores (cf. Table 6) were given to each thin-section based on its colour, original grain size, degrees of pyroxene and feldspar alteration, presence of epidote and apatite and the size and type of opaque grains present. Complete results and analysis of this novel quantitative approach are contained in Markham (2000).
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Last updated: Wed Jul 29 2009