On the basis that all stones are the result of folk being turned to stone by the powers that be (in my opinion, a far more sensible theory than sacred or lunar/solar alignments), perhaps this stone is an example of a black person being turned to stone. Given that black people would have been a rarity in the british isles in megalithic times, that may have been reason enough for the powers that be.
I think I've provided the answer to this one, haven't I?
