Olympic curling stones are made from granite found solely on one island off the coast of Scotland

During the 2026 Winter Olympics, interest in curling from fans in the United States has developed from curiosity to full-blown interest amid the mixed doubles team winning a silver medal on Tuesday and the women's team prevailing over Canada during Friday's round-robin session in Cortina. 

Much of the fascination with curling likely comes from being so different than other winter sports like skiing, skating, snowboarding and hockey. Why does the playing surface — called a sheet — look like a giant shuffleboard? Why are the players sweeping the ice? And what are those large stones that are slid down the rink toward the target — or "house"? 

The stones! Those large, heavy discs — weighing between 38 and 44 pounds — are not something fans would typically find in a sporting goods store or in an aisle next to the basketballs at Walmart. At least not a professional, competition-grade curling stone. The stones used for the Olympics are made in a small town factory by a company called Kays Scotland, which crafts the curling stones by hand for professional and Olympic competition.

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But the source granite used to make those stones is found in only one place, an uninhabited island located 10 miles off the country's coast named Ailsa Craig. Formed by a volcano 60 million years ago, the island — also known as "Paddy's Milestone" — is made up of dense granite, the stuff from which curling stones are created.

A remote island where curling stones are made sounds like a folktale or the stuff of mythology. But it's true. Ailsa Craig is made up of "microgranite" — formed from magma that cooled quickly, via The Athletic — that makes curling stones ideal for sliding on ice and staying intact when colliding with other stones during a match.

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Blue Hone granite, Common Green granite and Red Hone granite from the island is distinct from other granite seen and used around the world. The rock has tight molecular structures that make it water- and crack-resistant, according to NASA. That tight grain also helps the granite stand up to polishing and to "curl" as they glide along ice. 

Kays Scotland has exclusive rights to quarry Blue Hone, which is very water-resistant, and Common Green, resilient against colliding with other rocks at frozen temperatures, through 2050. The company, based in Mauchline, has been making curling stones from the granite for 175 years. 

As could be expected, the growing popularity of curling since becoming an official Olympic sport in 1998 has necessitated more granite be mined from Ailsa Craig. 

Originally, Kays Scotland quarried 210 tons of rock, enough for at least 1,000 curling stones. By 2013, the company was harvesting 2,500 tons of Common Green and 500 tones of Blue Hone, The Athletic reported. And according to Kays operations manager RIcky English, that amounts to taking "a teaspoonful" from an ice cream tub through the length of its agreement in terms of available supply.