Leaving Skara Brae this is along from the second passing place by the Loch of Skaill. Had to remove a veil of grass to ascertain it really was the thing I had previously found. To the right of it a stone is marked with that official bear's-paw 'sunburst' symbol, look for that. Still not 100% certain it is not geological or adapted natural still. IIRC it faces across to a very small unmapped 'islet' in the loch. Stone 'block'; straight 0.7m then 'niche'0.8m across and then it goes behind at an angle. Enclosing sides 0.5m and 0.7m long and 0.35m high, slab above 0.2m deep.
The OS position is imprecise because the site lies on a very plain stretch of the road alongside the Loch of Skaill. It seems strange that in this general area there is nothing noted apart from a quarry. I have called this a natural rock formation (despite its regularity) just to be on the safe side. But it does stand out as possibly man-made, perhaps the corner of something that mostly still is hidden by the road overhang on this section of road. Could it be a step in a wall? To me what one can see presents the appearance of a triangular niche for some unknown purpose of its own.