Also known as “Paddy’s milestone,” the island is actually a volcanic plug – a literal rock formed over an extinct volcano. And it turns out that the unique makeup of the rock left behind is uniquely suited for making curling stones. There are three subgroups of the water-resistant microgranite that can can be mined from the island: Ailsa Craig Common Green Granite, Ailsa Craig Blue Hone Granite and Ailsa Craig Red Hone Granite. Kays of Scotland has been making curling stones since 1851 and has the exclusive rights to the Ailsa Craig granite, which is why it has provided the stones for every single competition at the Olympic Winter Games. The blue hone, whose tight molecular structure makes it impervious to water and melting ice, is used for the insert and running band of the stone, while the green granite makes up the body.

Source: Huffington Post February 18, 2018 22:41 UTC