The remarkable properties and origins of the Olympic curling stone

Curling stones have changed considerably since the earliest recorded stories of ‘Scotland’s Ain Game’ being played on the frozen lochs and ponds of the northernmost country in Britain. In its earlier iterations, the stones would come in many shapes and sizes, and players would choose the most useful variation to sneak through a gap on the ice or cover the target - all with the aim of strategising victory.

Nowadays, the size of Olympic stones has been standardised, with each weighing 20kg with a width of 278mm and a height of 136mm.

However, some of the remarkable traditions related to curling stones continue to live on in the stones used in Olympic competitions today.

Where do Olympic curling stones come from?

“Every single Olympic curling stone comes from this little island off the coast of Scotland, called Ailsa Craig. And no other stone curls like an Ailsa Craig stone,” Erika Brown, the former Team USA skip explained in an article in Scientific America.

Curling stones are traditionally made of granite, a material found all over the world in regions as far-flung as Italy, the USA, India and the People’s Republic of China. However, for the sport of curling, nothing can replace the unique properties of the granite hewn from a quarry on the island of Ailsa Craig off of Scotland’s Ayrshire Coast.

The Ailsa Craig granite is some of the hardest and purest found in the world and maintains its shape despite the moist, wet conditions of the ice surface curling is played on.

Common green Ailsa Craig granite is used to create the body of the Olympic curling stone. Blue hone granite - another Ailsa Craig stone - is then fitted to the body to form the running band, which is the part of the stone that has contact with the ice. Resistant to cracking and condensation, the material perfectly fits a sport where a stone’s ability to glide on a surface in a consistent manner is paramount.

What’s special about Ailsa Craig?

Ailsa Craig is a small island that is 3.2km in circumference and said to have been formed by volcanic eruptions stretching tens of millions of years. As the magma cooled quickly it formed a smooth granite that makes up the surface of the island today.

In more modern times the island, which sits between Ireland and Scotland, has been the site of a 16th-century castle stronghold, an 18th-19th century prison and, most recently, a bird sanctuary featuring a large array of species including gannets, puffins and kittiwakes.

However, it is the molecular makeup of Ailsa Craig that makes it so uniquely suited to the sport of curling. No other destination in the world produces granite with the blend of heat and moisture resistance and hardy resilience than this small Scottish island.

Perhaps Brown best summed up the magic of Ailsa Craig with these words: “For us curlers, the island is a mystical place.”