3.5 Other samples from North Cornwall

Mr Dave Weddle, an experienced experimental knapper and stoneworker, discovered two large pieces of greenstone rock named MM3 (weighing 16kg) and MM4 (weighing >100kg), well away from known greenstone exposures in north-west Cornwall but relatively close to some Neolithic sites in the area. Macroscopic observation showed that these rocks appeared to have similar mineralogy and texture to greenstone axes, hence their inclusion in this article.

The thin-section from MM3 is very similar to GpI-1 and GpI-2, with partly altered partly ophitic clinopyroxenes and heavily altered feldspar. Abundant actinolite and cloudy epidote, coupled with patches of biotite, make up the groundmass of the rock thin-section.

Figure 27a and 27b
Figure 27: Sample MM3 in PPL and XPL (Field of View (FoV) 4mm). Click image to enlarge

Thin-sections from MM4 (MM4a-d) are very similar to GpI-6, with the addition of biotite and bright (xpl) amphibole totally replacing the non-ophitic pyroxene seen in MM4a-d. The groundmass consists of altered feldspar, with acicular actinolite and plentiful patches of granular biotite. Apatite is readily visible in these four thin-sections.

Figure 28a and 28b
Figure 28: Sample MM4 (MM4b) in PPL and XPL (FoV 4mm). Click image to enlarge


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Last updated: Wed Jul 29 2009