This Standing stone may not be all that ancient, I was bumming around the Canmap and came across this discription of the stone -
At NM 5434 2820 is a wedge-shaped standing stone 2.1m high by 2.5m in girth at the base. It does not appear to be a prehistoric standing stone and is possibly one of a series of marker stones along the pilgrim route from Green Point to Iona.
Visited by OS (R D) 2 June 1972.
I hope they're wrong, though Iv'e got nowt against pilgrim routes specially if it takes you somewhere as neat as Iona.