>> "shiny black appearance"

Could fit my thoughts ... almost.

I'm not even sure the one in Edinburgh is the Stone of Scone. When it was stolen in the 50s (or was it the 60s? need to check notes it's been a year or so) there were so many factors that could mean the real one was swapped out, but you probably know all about it falling out of the Ford Escort and the wonderfully funny peat cutting episode and a relative of one of the liberators being a stone mason.