Did you know that every curling stone ever used in the Olympics has come from this tiny island: Ailsa Craig. It is located 10 miles west of mainland Scotland. It has the perfect granite to withstand the impact under curling conditions. Most ganite is too quartz-rich. This island is also known as Paddy's milestone. The island is a volcanic plug. A volcanic plug, also called a volcanic neck or lava neck, is a volcanic object created when magma hardens within a vent on an active volcano. When present, a plug can cause an extreme build-up of pressure if rising volatile-charged magma is trapped beneath it, and this can sometimes lead to an explosive eruption.