Curling Power Play: The Science Behind the Stones
February 10, 2026 – The Winter Olympics showcase incredible athleticism, but often overlooked is the fascinating science behind the equipment. Take curling, for example. The seemingly simple stones used in this strategic sport aren’t just any rocks; they come from just two locations on Earth: a small island in Scotland called Ailsa Craig and the Trefor granite quarry in Wales. But what makes these stones so uniquely suited for gliding across the ice, and are they truly irreplaceable?
To uncover the secrets behind these iconic stones, Scientific American spoke with Derek Leung of the University of Regina in Saskatchewan, a mineralogist and former Team Hong Kong curler. Leung has combined his passions by conducting the first mineralogical analyses of curling rocks in over a century.
The Anatomy of a Curling Stone
A curling stone consists of two key surfaces: the running surface, which skids across the ice, and the striking surface, used for collisions with opposing stones. Each surface requires specific properties to perform optimally. This is where Ailsa Craig and Trefor come into play.
Ailsa Craig has been the source of curling stones since the early 19th century, while Trefor gained prominence after World War II. Both locations yield four types of granitoid rocks: Ailsa Craig common green and blue hone, and blue and red Trefor. These rocks are igneous, formed from cooling magma or lava.
Interestingly, Leung’s research suggests that younger rocks are preferable. “Having a young rock is probably a good thing because it’s less likely to have incurred stresses related to different tectonic events” before the stresses of the game are applied.
Debunking the Quartz Myth
Common belief held that the ideal curling stones contained minimal quartz, a brittle mineral. However, Leung’s analysis revealed that all four rock types do contain quartz. Surprisingly, he found “almost no fractures,” likely due to the rocks’ relatively young age.
The Perfect Surfaces
Ailsa Craig blue hone is typically used for the running surface. Manufacturers insert a disk of this material into the bottom of the stone. Its small, uniform grain size minimizes chipping and ensures consistent sliding. It’s also relatively nonporous, preventing water from causing fractures.
For the striking surface, larger grain size is preferred. “You want to have larger differences in grain size,” Leung explains, “because it prevents certain types of damage from occurring” during collisions. Ailsa Craig common green, blue Trefor, and red Trefor all fulfill this requirement.
The Future of Curling Stones
The 2026 Milano Cortina Winter Olympics will feature stones made of Ailsa Craig common green with blue hone running surfaces. While Ailsa Craig is now a protected bird sanctuary and blasting is prohibited, the search for alternative sources is underway.
Past attempts to find replacements, like the anorthosite from Northern Ontario, proved unsuccessful due to chipping. However, with a better understanding of the ideal rock properties, Leung believes a new source could be found. He suggests exploring areas with similar geological formations to Ailsa Craig, such as Nova Scotia.
“We could look for rocks that are formed in a similar environment as Ailsa Craig,” Leung says. He hopes to collaborate with quarries to analyze potential candidates and even test them on the ice.
Source: Scientific American
