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Monday, 2 November 2015

Three Stonehenge stumps

This is a very poor quality image, from the Atkinson Stonehenge collection.  The annotations are mine.  Standing bluestone 33 is at the edge of the pit.

There has been much speculation (not from the geologists, who have been rather careful) about "two Stonehenge bluestones" being transported from Rhosyfelin and put in position at Stonehenge.    These obviously have to be made of foliated rhyolite, and the only candidates here are stumps 32d and 32c, since they actually look as if they are foliated or laminated, with a broken and crumbly top surface in each case.    Stump 32e looks quite different, and as I have said many times before it looks rather like a dolerite.

These stumps have never been sampled or analysed properly, so they are somewhat mysterious.  That's very frustrating, since they are only just under the ground surface, and it would take just a few minutes of work to get down to them and to take samples -- but EH is not being particularly cooperative, for reasons that are unclear.

To repeat, the only things from Stonehenge to have been provenanced to the Rhosyfelin area are fragments of stone found in the debitage in the soil layer.  The geologists have suggested that all this debris might have come from the destruction of one or two standing stones -- but at the moment that is pure speculation, until stumps 32c and 32d can be sampled and matched up with analysed and identified fragments.


Myris of Alexandria said...

32c in other photos looks like volcanic group A in the pet rock boys revised nomenclature. Best to wait until Ixer and Bevins 2016 is published.
32d has a strong planar fabric and may be Cryf. This is most people's choice.
32e has a planar fabric look to the left of caption. This would be unusual for the dolerite plus Atkinson he, the photographer, called it rhyolite check in the book certainly did NOT call it dolerite, not 33 is a dolerite and next to it.
I can now see an argument for saying perhaps two from CRyf.
You have scored an own goal.

BRIAN JOHN said...

An own goal? I couldn't care less, one way or the other. Just an interesting little geological problem.

BRIAN JOHN said...

Yes, I can see the slight traces of diagonal banding / foliations, even though the quality of the pic is lousy. Could it be a volcanic ash? I have seen plenty of boulders in the area with that sort of surface expression.....

On the other hand there are dolerites on Carningli and elsewhere that do have clear banding in them, picked out by weathering. Would they then be called flow-banded dolerites? Will post some pics....