Largely as a result of media hype generated by Prof MPP and his colleagues, the large stone at Rhosyfelin which was first unearthed in 2011 has gained considerable notoriety. It is known to thousands of faithful followers as "the bluestone that never made it to Stonehenge" or as "the bluestone that confirmed the presence of a Neolithic quarry at Rhosyfelin."
On p 286 of his 2012 book, Prof MPP refers to "an ancient ground surface", "hammer stones" and "a monolith left behind when quarrying ended" as showing that this is "the Pompeii of prehistoric stone quarries." All a bit over the top, you might think. But warming to his task, the good professor then says of the discovery of the stone: "This was the smoking gun; the game was up for anyone still trying to argue that the bluestones were not quarried in Preseli during the Neolithic, and then taken to Wiltshire....."
In the midst of all this excitement, let's take a deep breath and take a look at the famous stone, leaving aside all the speculation about fulcrums and rails, pillars and wedges and so forth.
The facts about the stone
As I have already indicated, it is made of local blue foliated rhyolite. It is over 3m long and is probably twice as heavy as Prof MPP suggests -- at around 8 tonnes. So it is much larger than any of the Stonehenge bluestones, and on that basis alone one might wonder how on earth our heroic Neolithic ancestors planned to get it out of the Brynberian Valley and all the way to Stonehenge, all in one piece. That would have been a Herculenean task, even if the rock was solid and robust, which it is not......
So let's take a look at it in detail. We can of course only see five of the six sides, since its bottom face is hard to examine without risking life and limb. The elongated, roughly rectilinear stone lies approximately E-W, so we can refer to the faces as "E,W, N, S and top" without any great risk of confusion. The E and W faces are the "ends" of the rock and the N and S faces are the elongated "sides".
Here is a photographic record:
[Further Note added: we had an interesting discussion in 2012 -- thanks to Phil Morgan -- on the rock mechanics of the site, reported here:
The diagrams are particularly helpful. There were also lots of useful comments.]