The unspotted dolerites at Stonehenge

Stone 44 at Stonehenge (photo: Simon Banton). Unspotted dolerite -- or maybe spotted dolerite, depending on which text you are looking at.  From Carn Ddafad-las?  Weight c 1 tonne. A highly abraded and weathered boulder.

Stone 45 at Stonehenge (photo: Simon Banton).  Unspotted dolerite, source Carn Ddafad-las (maybe) or Cerrigmarchogion (maybe) and weight c 1 tonne. A highly abraded and weathered boulder, somewhat elongated.

The base of standing stone 62, somewhat damaged by rock collectors in recent centuries (photo: Simon Banton).  Unspotted dolerite, and  characteristics different from stones 44 and 45, but still classified as "group 2 dolerite".  This one is a very fine standing stone, clearly shaped and placed in the bluestone circle.  Ixer and Bevins speculate that it might have come from Carn Meini or Carn Gyfrwy, or maybe from Cerrigmarchogion or Talfynydd........   Parker Pearson speculates that this stone has a "footprint" similar to one of the supposed sockets at Waun Mawn, and argued that the stone was first used at Waun Mawn and then moved to Stonehenge -- but I have looked at the pit in the ground surface and I don't think there is any matching at all......... 

Simon's very useful web site is here:

http://www.stonesofstonehenge.org.uk/p/about-this-site.html

We can argue, maybe, about the origins and the transport and the shaping of Stone 62, but there can surely be no argument at all about stones 44 and 45.  There is no way that these could be quarried bluestone monoliths, and they are typical glacial erratics with heavily abraded surfaces and rounded off edges.

Anthony Johnson's excellent plan showing where the numbered stones are located.

In the literature there are some interesting comments on the Boles Barrow bluestone, which is a spotted dolerite but which seems to have more in common, geochemically, with the unspotted dolerites numbered SH44 and SH45. Thorpe and Williams-Thorpe thought that the Boles Barrow bluestone might have come from near Carn Ddafad-las, right on the edge of the spotted dolerite terrain.  This may support the contention that there is great variation within dolerite intrusions related to depth or cooling rate, suggested by a number of different researchers.   It may even be that both spotted dolerites and unspotted dolerites can occur within the same intrusion, making accurate provenancing of Stonehenge samples quite difficult.

This is quite helpful too -- a map kindly posted on Twitter by Mike Pitts last year, confirming just three unspotted dolerites and lots of empty spaces:

There are just 3 known unspotted dolerite monoliths at Stonehenge -- one standing and two recumbent.  However, there are also some bits of debris in the debitage.  Information from studies of fragments has fed into this analysis.

"Revisiting the provenance of the Stonehenge bluestones: Refining the provenance of the Group 2 non-spotted dolerites using rare earth element geochemistry." 2021.  Journal of Archaeological Science: Reports 38:103083  by Richard Bevins, Nick Pearce and Robert Ixer

https://www.researchgate.net/publication/352508571_Revisiting_the_provenance_of_the_Stonehenge_bluestones_Refining_the_provenance_of_the_Group_2_non-spotted_dolerites_using_rare_earth_element_geochemistry

Extract from the Abstract:

Group 2 non-spotted dolerites are now divided, on the basis of their REE (rare earth elements) contents, into four Preseli and two Stonehenge sub-groups, (Groups 2i-2iv and Groups 2v-2vi, respectively) while Stonehenge orthostat sample SH44 plots apart from all other Stonehenge and Preseli samples in all discriminant diagrams used. The new data show that Preseli Group 2i dolerites have very distinct concave down “humped” patterns and bear no resemblance to any analysed Stonehenge dolerites. The source of Stonehenge Group 2v dolerites remains equivocal; they plot close to Preseli Group 2ii dolerites from Carn Ddafad-las and Garn Ddu Fach and have in common the presence of notable positive Eu anomalies, but they show minor differences, especially in relation to their Gdn/Ybn ratios. However, Stonehenge orthostat sample SH45 shows a near identical REE composition to Preseli Group 2iii dolerites from Cerrigmarchogion. In terms of the interpretation of REE contents and chondrite-normalized patterns we found no differences whether using the ‘standard’ techniques used by geochemists, based on chondrite-normalized elemental ratios and values, or the quantitative approach using shape factors derived from polynomial curve fitting.