The Source of the Altar Stone Fragment

As part of the 1958 excavation of Altar Stone, Stone 80, a series of photographs were taken of the exposed stone. 

Only one of them is publicly available from the Historic England archive, and whilst it isn't the clearest of the series, it does show the break in the stone clearly. 

And the space where Captain Richard Beamish removed the sample that is now in Salisbury Museum and is the fundamental in the recent analysis of the stone. 

The size and shape is correct and a similar loose fragment is still there. Without excavation and refitting it, which will never be allowed, I can't be 100% certain, but it does prove that the Altar Stone is the physical as well as the geochemical match to the sample.