Ailsa Craig is a small granite island in the Firth of Clyde, about 16 kilometers off the coast of Scotland. The island, also known as “Paddy’s Milestone” for its location halfway between Glasgow and Belfast, was a haven for Catholics during the Scottish Reformation in the 16th century. Today, its uninhabited and a bird sanctuary home to large numbers of various species of birds including gannets, razorbills, kittiwakes, herring gulls, shags, fulmars, puffins and black -backed gulls.
Ailsa Craig is also the world’s major supplier of a rare type of micro-granite with a highly-interlocked, finely-grained mineral structure free of quartz, which is used to make stones for the sport of curling. More than two-thirds of all curling stones originate from this tiny volcanic pug. The other being the Trefor Granite Quarry in Wales.
Curling is a very unusual sport played on ice that has a unique mix of shuffleboard and bowling on ice. It involves two teams of four players each, who take turns sliding massive, polished granite stones across the ice towards a target. The goal is to place the team’s stones closer to the target than the opponent team. The game was invented by the Scots more than 400 years ago, and is now a regular event in the Winter Olympics. It’s very popular in Canada, being the third-most watched sport on Canadian television behind ice hockey and gridiron football.
The granite blocks used to play the game cannot be manufactured from just any granite. The stones are very heavy, between 17 to 20 kg, and they crash against each other repeatedly during gameplay. Ordinary granite would crack, but not the type quarried from Ailsa Craig.
Ailsa Craig is a volcanic plug borne out of a long extinct volcano that erupted some 60 million years ago. The younger sedimentary rocks covering Southwest Scotland have long since been eroded away leaving behind the hard igneous rocks of the island. The island is about 1.2 km long and 0.8 km wide, and rises steeply to an elevation of 340 meters. Being located at a strategic position in the channel between Ireland and Scotland, the island has a long history going back to the late 1500s when a castle was built here to protect the island from Spanish invaders. The castle, now ruined, still stands on the island, along with a small cottage, a lighthouse and a granite quarry operated by Kays of Scotland, who has exclusive rights to the Ailsa Craig granite.
Ailsa Craig produces two types of granite for curling — Blue Hone and Common Green. Blue Hone has very low water absorption, an important attribute when running on ice, which prevents the action of repeatedly freezing water from eroding the stone. Ailsa Craig Common Green is of lesser quality than Blue Hone, but both are extremely durable, non-porous, and shatter-resistant. A curling stone made from Ailsa Craig granite has an average lifespan of 20 to 30 years. Many lasts longer. There are stones in use today that were quarried 40 to 50 years ago.
In the past, most curling stones were made from Blue Hone but the island is now a wildlife reserve and quarrying is restricted. But every few years the company is allowed to return to the island to collect stones. The last harvest of Ailsa Craig granite took place in 2013, after a hiatus of 11 years. The company is said to have harvested 2,000 tons of stone sufficient to fill anticipated orders until at least 2020.
Today, most curling stones are hybrids, made from both Ailsa Craig granite and Trefor granites.
Curling stones. Photo credit
A player about to deliver a stone at a curling match in the 2010 Vancouver Olympics. Photo credit
Men curling in Toronto in 1909. Photo credit
A curling stone tops one of the gateposts at the Barskimming Road works of Kays of Scotland. Photo credit
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