Curling Stones: A Precious Resource

Copyright: J. Durnan, for reuse under the Creative Commons Attribution-Share Alike 2.0 Generic licence.

Ailsa Craig is the little white dot at the south end of the Firth of Clyde.

Ailsa Craig.  A formidable, solitary, dome-shaped rock island lying in Scotland’s Firth of Clyde 16 km (10 mi) off the Ayrshire coast.  Uninhabited since 1990 (though the lighthouse and a few buildings remain, and sightseeing boats makes regular trips), it’s now a nature preserve and the small island is a haven for seals, puffins, gulls, and around 40 000 gannets.  It’s also home to one of the rarest, hardest-to-find materials on Earth.  Ailsa Craig, you see, has produced approximately 60 to 70 percent of the world’s curling stones currently in use.


The other side of Ailsa Craig, where granite boulders are harvested every few decades in order to provide material to make curling stones.  Source: baaker2009,  Licensed under the Creative Commons Attribution 2.0 Generic (CC BY 2.0) licence.


Source: K. Funakoshi, for reuse under the Creative Commons Attribution-Share Alike 2.0 Generic licence.

Curling stones, you say?  As in curling, the ice-based target sport developed by the Scots, adored by Canadians (it’s the third-most popular sport on Canadian television behind ice hockey and gridiron football, and 1.2 million of the world’s 1.5 million curlers live in Canada), and looked upon with wonder and bemusement by most of the rest of the world.  It’s not often that sport crosses paths with geology, but when your sport is built around quarried granite boulders, it’s a fairly major intersection.

The large stones used to play the game are made of granite, and not just any old type of granite can be used to make these 17-20 kg (38-44 lb) rocks.  During gameplay, the stones crash against each other repeatedly.  Used over and over again for years on end (20-30 years is a healthy lifespan), an average curling stone sees thousands of such collisions over its lifespan, meaning that the type of granite used has to be extremely durable, non-porous, and shatter-resistant.  Such rock is extremely hard to come to come by, and traditionally the only two suitable types of granite for curling, blue hone and common green, were only found on Ailsa Craig.

Ailsa Craig is an exposed volcanic plug sticking out of the ocean, formed around 500 million years ago.  Much of the rock is composed of certain types of micro-granite, a highly-interlocked, finely-grained mineral structure free of quartz, specifically blue hone and common green.  Blue hone is considered to be the highest quality granite of the two because of its low water absorption (an important attribute when running on ice) as opposed to common greenBlue hone is used as the bottom part of the stone that runs along the ice (the running band) while common green composes the main body of the stone.

The issue with quarrying rock from Ailsa Craig is that it also serves as a privately-owned nature preserve leased by the Royal Society for the Protection of Birds.  Active blasting of rock at the island’s granite quarry has been banned for many years on the island.  There are two main manufacturers of curling stones: Kays of Scotland and Canada Curling StoneKays have an exclusive agreement with the island’s owner, the Marquess of Ailsa, to harvest the loose boulders still extant on the island, most recently removing rock in 1989 and in 2002.  The most recent harvest removed 1 500 tonnes of common green and 200 tonnes of blue hone – enough to make about 8 000 stones, which would be enough to supply 500 rinks – a decade’s worth of business for the company.  Some of the slabs of granite can be seen in their workyard on Google Street View here.

With only Kays allow to harvest from Ailsa Craig, if you’re Canada Curling Stone, Kays’ main competitor, it’s especially important to find a new location that provides suitable granite.  The search has been on for many years around the world to find suitable replacement granite, but the only place found so far is on the Llŷn Peninsula in north Wales at the Trefor quarry.  Not only do Canada Curling Stone have the exclusive rightto harvest Trefor granite, but the supply of rock available is far greater.  Trefor is more durable than Ailsa Craig blue hone and so is better suited for crashing and banging, but Ailsa Craig blue hone is less porous and better suited for sliding on ice. Today, many rinks are moving to a sort of hybrid stone: stones with traditional Ailsa Craig blue hone running band inserts (the smoothest, least-porous type of granite for gliding along the ice) attached to Trefor bodies and strike bands (the middle portion of the stone that collides with other stones) along the outside.  A hybrid stone as such can extend the lifespan of the stone to 40-50 years.

The Trefor quarry in north Wales.

It’s important for curling clubs, especially in smaller communities where funds at the local curling clubs may be limited, to have stones that can last a long time as purchasing new sets of stones can be quite expensive (a new quality set of 16 Trefor stones costs around CDN$10 000, and even the cheap ones range in the CDN$6-7 000 range).  Stones can be repaired to a degree (also not cheap), but only so much can be done before the integrity of the stone is lost.  With the continued growth of the sport around the world due to its exposure via the Olympics, it should be interesting to track this cottage industry and to see if any other companies try to enter the marketplace with their own supplies of special granite.

On a side note, the Marquess of Ailsa listed the island for sale in May of 2011.  The price? £2.75 million (US$4.34 million).

Further Reading

Canadian Curling Association (2012).  The History of Curling.  Available at  Accessed 21 February 2012.

Canada Curling Stone Co. (2012).  Granite Types.  Available at  Accessed 21 February 2012.

Kays of Scotland (2012).  About Us.  Available at  Accessed 21 February 2012. (2002).  Ailsa Craig Photogallery.  Maybole Home Page.  Available at  Accessed 21 February 2012.

Mount, H. (2011).  Wanted: One very wealthy twitcher to buy this £2.5m island ruled by birds.  Daily Mail, 4 May 2011.  Available at  Accessed 21 February 2012.

Roach, J. (2004).  Puffins Return to Scottish Island Famous for Curling Stones.  National Geographic News, 27 October 2004.  Available at  Accessed 21 February 2012.

Stouwdam, H. (2010).  Not just any rock: curling stones’ special granite comes from Scotland.  NRC Handelsblad, 17 February 2010.  Available at  Accessed 21 February 2012.

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One thought on “Curling Stones: A Precious Resource

  • Fascinating! I'm Canadian, my parents curled and I never knew how curling stones were made or from what they were made! Thanks for including the link to the back yard of the Ailsa Craig property showing the slabs, I had been wondering as I was reading what the collected rock looked like.

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