Curling stones, a crucial element of the Olympic sport of curling, originate from two unique sources: Ailsa Craig in Scotland and the Trefor granite quarry in Wales. These stones, each weighing approximately 40 pounds, are specifically selected due to their unique geological properties that enhance their performance on the ice.
The science behind curling stones was explored in-depth by Derek Leung, a mineralogist and competitive curler, who conducted the first comprehensive analysis of these rocks since 1890. He sought to understand what makes the stones from Ailsa Craig and Trefor so suitable for the sport. The design of curling stones consists of two main components: the running surface, which glides across the ice, and the striking surface, which interacts with other stones.
Historically, Ailsa Craig has supplied curling stones since the early 19th century, while Trefor became popular after the sport’s resurgence in popularity post-World War II. Each location provides two varieties of stone: the Ailsa Craig common green and blue hone, along with the blue Trefor and red Trefor. These rocks are classified as granitoids, igneous types formed from molten magma millions of years ago. Notably, Leung found that their relatively young geological age contributes to their structural integrity, making them less prone to flaws or fractures that could impact their performance.
Contrary to the traditional belief that a minimal presence of quartz, a brittle mineral, was essential for curling stones, Leung discovered that all four types of rock actually contain quartz. However, these stones’ young age appears to minimize any fracturing, resulting in a robust structure. The blue hone, often used for the running surface, boasts fine, uniform grain sizes that allow for smoother sliding, which is vital for the sport’s precision.
The striking surface benefits from a contrast in grain sizes, as larger grains prevent specific types of damage during collisions. Both Ailsa Craig common green and the Trefor variants fulfill these requirements, contributing to their role in the main rock of curling stones. For the upcoming 2026 Milano Cortina Winter Olympics, stones will utilize Ailsa Craig common green combined with blue hone for optimal performance.
While Ailsa Craig and Trefor are currently the go-to sources for curling stone material, Leung’s research suggests that it is possible to find suitable rock from other regions. Indeed, historical evidence indicates that various stones were used in curling’s early days in Scotland. As Ailsa Craig is now a protected bird sanctuary, exploring additional sources is essential for the future of curling.
Looking ahead, Leung aims to collaborate with quarries to analyze potential new materials. He believes that with advancements in mineralogical knowledge, suitable rock can be found in other locations, such as Nova Scotia. This effort may unlock new possibilities for curling stones, ensuring that this beloved sport continues to thrive for generations to come.