The Constantine Palaeologos Research Fund's generosity has enabled Rob Ixer and Richard Bevins to further elucidate the types of stones at Stonehenge in the current edition of WAHNS - an article for serious Stonehenge Geeks only.
Volcanic Group A Debitage: its Description and Distribution within the Stonehenge Landscape
by Rob A. Ixer and Richard E. Bevins
Abstract: The three major groups of debitage found in the Stonehenge Landscape are dolerites, rhyolitic tuffs (almost exclusively from Craig Rhosyfelin) and ‘volcanics with sub-planar texture’. This last group comprises two separate lithological sub- groups namely, Volcanic Group A, friable rocks with abundant white mica and a strong metamorphic fabric, and very rare Volcanic Group B hard rocks that are characterised partially by an unusual mineralogy including graphitising carbon. Petrography, whole rock X-ray diffraction and whole rock geochemistry suggest that Volcanic Group A is a coherent group representing a single lithology, namely an argillaceous lithic tuff and that it is quite different from Volcanic Group B (including Stonehenge orthostat SH38) and from Stonehenge orthostat SH40. Spatially, as with the other major debitage groups, Volcanic Group A lithics are widely and randomly distributed throughout the Stonehenge Landscape; temporally, almost none of the debitage has a secure Neolithic context. The debitage cannot be matched to any above-ground Stonehenge orthostat but may be from one or more of ﬁve buried and, as yet, unsampled stumps. The lithology is believed to be from an unrecognised source on the northern slopes of the Preseli Hills but perhaps not from Foel Drygarn as has been suggested