What is the name of a Scottish island where granite to make curling stones is quarried?

Ailsa Craig is also familiarly known as Paddy's Milestone as it stands isolated in the Firth of Clyde sort of midway between Glasgow and Belfast and would have been a marker on the old steamer routes.

Something I would have found boring when I was young. But now I can appreciate the skill and strategy. I just wish I could've played it myself.