I wonder what kind of rock is used for megaliths? Is it whatever is at hand? Granite in the UK, maybe limestone in places like Malta. ?
In The Megalithic Empire
we argue in two cases that granite megaliths were specifically made. In Carnac (Brittany) and at Merrivale (Dartmoor) granite was mined and megaliths fashioned, in both cases for export elsewhere. If granite can be reliably sourced to a particular place in the same way that (allegedly) bluestones and gold can be, this should be easily proved/disproved.
Nobody has been able to show that blue-stones are anything special. Nor for that matter is granite so wondrous that shifting it long distances makes it so obviously worthwhile. And yet we have much later history that shows for some reason people would shift Caen stone to London (or whatever) for no obvious reason other than prestige. So, on the principle 'What is is what was..."