Geologist conversation

Just listening over the way to some of my geotech colleagues:

Garth (just back from holiday): Peter, I will buy you lunch if you can guess the significance of this rock.

{Hands over small bit of, well, rock, sort of flint like I guess? It's a rock.}

A few clues are discussed, ie a general region and the fact that it’s significant in this country’s history

Peter: Ah, ok, hang on… is it…. from the quarry where the rocks that formed Stonehenge were taken?

Garth: Yes! I owe you lunch.