The strange geology behind the Olympic curling stones

The strange geology behind the Olympic curling stones

by Andrea Thompson Edited by Seth Fletcher

From skating to curling, there’s a lot of science behind the exciting sports of the Winter Olympics. to follow Our coverage is here To know more.

Athletes often have special equipment or apparel to run, swim, skate or ski, but curling takes things to another level. The Curling Rocks – as the round, nearly 40-pound stones are called – come from only two places on the planet: a small island in Scotland called Ailsa Craig and the Trefor granite quarry in Wales.

But what is it that makes the rocks in these places uniquely suited to sliding across a rectangular slab of ice toward a bullseye target? And are these really the only places to find suitable stones?

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To find out, scientific American spoke to Derek Leung of the University of Regina in Saskatchewan, a mineralogist and avid curler who competes for Team Hong Kong. Leung combined his two interests by conducting the first mineralogical analysis of curling rocks since 1890. “It’s been over a hundred years since we’ve seen them,” he says, so he wanted to see what modern science could tell us.

But before we get into that, let’s take a look at the two main parts of a curling rock: the running surface and the striking surface. The first rock has a ring at the bottom that slides on the ice, and the second rock has a band around the edges that bounces off other rocks (ideally knocking the opponent’s rock off the bull’s eye or pushing your team closer to it).

Every surface requires specific properties to perform its function. This is where Ailsa Craig and Trefor Quarry come in. The former has been used for turning stones since the early 19th century; Curling increased in popularity after World War II.

There are two types of rock at each location that are used for turning stones: Ailsa Crag normal green and Ailsa Crag blue hone, and blue trefor and red trefor. All four types are granitoids, which are igneous rocks, meaning they form when magma or lava cools and crystallizes. The rocks of Ailsa Craig were formed about 60 million years ago when magma moved into a relatively shallow layer of the Earth’s crust during the rift that created the Atlantic Ocean. Trefor was formed about 400 to 500 million years ago during a mountain-building event called the Caledonian orogeny. Geographically both are quite young. “Having young rock is probably a good thing because it means it is less likely to have stress related to various tectonic events on it before it is subjected to curling stress,” says Leung.

Common wisdom holds that the rocks from these two sources were ideal because they contained very little quartz, a brittle, silica-based mineral that would be less than ideal for expensive stones that constantly collide with each other. (Curling stones cost about $600 a pop, and they’re typically used for 50 to 70 years.) But Leung found that all four rocks actually contained quartz. Yet under the microscope, “I found almost no fractures,” he says, possibly due to his young age.

Ailsa Craig Blue Hon is commonly used for running surfaces; The makers cut a circle out of the bottom of the main rock and inserted a disk of blue hone. Leung found that blue hone has small, fairly uniform grain sizes. This is ideal for sliding on ice for decades, as larger mineral particles are more likely to dislodge from the ice, leaving holes in the surface that can cause unpredictable behavior. Blue horn is also relatively non-porous, meaning the ice is less likely to let water through and cause fractures.

For the striking surface, on the other hand, “you want a larger difference in grain size,” Leung says, because “this prevents certain types of damage from occurring” when the stones strike. Ailsa Craig Normal green, blue trefor and red trefor are all good for this, which is why they are used for the main rock; The attractive surface is carved out of the main rock. The rocks for the 2026 Milano Cortina Winter Olympics will be made from Ailsa Craig mango green and blue hone will be used for the running surface.

In theory, there is no reason why rocks from other locations couldn’t work for curling. After all, when that 1890 study was conducted, curlers used stones from all around Scotland, the birthplace of the game. The Ailsa Craig and Trefor granite quarries probably became the preferred sources over time through some combination of their performance characteristics, tradition and standardization. And blasting is no longer permitted in the secluded bird sanctuary, Ailsa Craig, so another source will help keep curling clubs stocked in the future.

This is something Leung hopes to work on. An attempt in Canada in the 1950s failed because a very dark, igneous rock called anorthosite quarried from northern Ontario began flaking soon after use. But with better knowledge of which rocks work best, it may be possible to find a new source. Leung says, “We could look for rocks that formed in a similar environment to Ailsa Craig — perhaps Nova Scotia, which is on the opposite side of the Atlantic rifting event that created the granitoids found at Ailsa Craig.

He hopes to one day work in the mines to obtain samples for analysis. If he finds any potential candidates, he’d like to make them into curling rocks and try throwing them under the snow to see what happens.

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