Granite Island Ailsa Craig: The Secret Behind Curling Stones

Ailsa Craig, a remote and uninhabited island located 10 miles (16 kilometers) off the southwest coast of Scotland, continues to play an essential role in the Winter Olympics as the source of the rare granite used to craft curling stones.

Kays Curling, based in Mauchline near Ayr, holds the exclusive license to harvest granite from the island. The company has supplied stones for the Winter Games since curling debuted as an official medal event in 1924 in Chamonix, and has continued that tradition since the sport returned in Nagano in 1998. According to co-owner Jim English, the company’s stones have likely been behind every gold, silver, and bronze medal won since then.

During routine inspections on Ailsa Craig, English evaluates granite boulders for cracks and surface flaws. The island contains two unique types of granite — common green, used for the main structure of the stone, and blue hone, known for its waterproof and dense qualities, used on the running surface that slides across the ice. These features make the material ideal for curling, where stones must withstand repeated collisions and extreme cold without splitting.

Geologists believe the microgranite on Ailsa Craig was formed by volcanic activity millions of years ago. Its elasticity helps absorb energy during impacts, while the blue hone granite ensures smooth, consistent performance on ice. Experts say this particular type of granite cannot be found anywhere else in the world.

Harvesting methods vary. Common green granite typically falls naturally and is collected in large pieces weighing up to 10 tons. Blue hone requires controlled extraction using gas charges to break rock along natural cracks, producing smaller blocks under two tons. The stones are transported to Girvan Harbour, sliced into circular forms, and processed by Kays. Finished stones weigh about 42 pounds (19 kilograms). A single-insert stone costs £704 ($930), while a double-insert model costs £750 ($990). A full set of 16 double-insert stones is priced at £12,000 ($15,860).

Environmental protection remains a priority. The island is home to significant gannet populations and gray seals. Strict precautions are taken to prevent rodents from reaching the island, with rat traps deployed to protect local wildlife.

Curling’s popularity is expanding globally. Kays produces between 1,800 and 2,000 stones annually, with Canada as its largest market. Demand is rising in China, Japan, and South Korea, especially following the 2022 Beijing Winter Olympics. The company has also delivered stones to unexpected locations such as Qatar and Antarctica, where curling is offered as part of luxury travel experiences.

With the upcoming Milan Cortina Winter Games, Ailsa Craig’s unique granite will again be at the center of Olympic curling — reinforcing the island’s lasting and influential legacy in the sport.