Ailsa Craig: The Island That Makes Curling Possible

Every four years, when the Winter Olympics roll around, millions of people tune in to watch curling for the first time. They're fascinated by the sweeping, the strategy, the shouting. But most viewers miss the most remarkable part of the sport: those heavy granite stones sliding across the ice come from a single uninhabited island off the coast of Scotland.

Not most of them. Not many of them. ALL of them.

Every single curling stone used in Olympic competition since 1924 has been made from granite quarried from Ailsa Craig, a tiny volcanic island 10 miles off Scotland's coast. The island is just 0.75 miles by 0.5 miles, rises 1,120 feet out of the water, and has no permanent human residents. Just thousands of seabirds, a medieval castle ruin, and the world's only supply of granite that can make a proper curling stone.

The island's Gaelic name translates to "fairy rock," and there's something almost magical about it. Because while granite exists all over the world, nothing curls quite like an Ailsa Craig stone. "Every single Olympic curling stone comes from this little island off the coast of Scotland, called Ailsa Craig," explained Erika Brown, former Team USA skip. "And no other stone curls like an Ailsa Craig stone."

This is the story of an island, a rock, and why 60 million years of geology made curling possible.

What Is Curling?

Before we talk about the stones, let's quickly explain the sport.

Curling is basically shuffleboard on ice with 44-pound granite rocks. Two teams of four players take turns sliding stones down a 150-foot sheet of ice toward a circular target called the "house" (like a bullseye). The goal is to get your team's stones closer to the center than your opponent's.

The twist? Team members use brooms to frantically sweep the ice in front of the moving stone, which slightly melts the ice and changes the stone's speed and trajectory. It's weird, strategic, and oddly captivating once you understand what's happening.

Curling dates back to the 16th century in Scotland, making it one of the oldest team sports in the world. Medieval Scots would slide heavy river stones across frozen ponds and lochs. Eventually, people started shaping stones specifically for the game. And after trying granite from all over Scotland, they settled on one source: Ailsa Craig.

The sport became so formalized around Ailsa Craig granite that when curling became an official Olympic sport in 1998 (after being a demonstration sport several times earlier), the rules required stones from the island. They've been used in every Winter Olympics since 1924.

The Island: Ailsa Craig

Ailsa Craig sits in the Firth of Clyde, about 10 miles west of the Scottish town of Girvan. On a clear day, you can see it from the mainland, a distinctive dome-shaped rock rising dramatically from the sea.

The island formed about 60 million years ago during the breakup of a supercontinent. As North America, Greenland, and Europe separated to form the Atlantic Ocean, volcanic activity surged. Magma pushed into shallow layers of the Earth's crust and cooled relatively quickly, forming the microgranite that makes up Ailsa Craig.

This volcanic origin is crucial. The rapid cooling created a very fine-grained, dense granite with unique properties.

A History Beyond Curling

Ailsa Craig has a fascinating past beyond curling stones:

Medieval stronghold: A 16th-century castle was built on the island, likely as a defensive position.

Prison: In the 18th and 19th centuries, the island briefly served as a prison.

Lighthouse: An unmanned lighthouse operated on the island to guide ships through the Firth of Clyde.

Bird sanctuary: Today, Ailsa Craig is a protected nature reserve managed by the Royal Society for the Protection of Birds (RSPB). It hosts Scotland's third-largest gannet colony, along with puffins, guillemots, kittiwakes, razorbills, and various gulls. The bird population is why quarrying is strictly limited.

The island is privately owned by the Marquess of Ailsa (part of the Kennedy family, who've held the title since the 18th century). They've granted exclusive rights to harvest granite to one company: Kays of Scotland.

Kays of Scotland: The Only Curling Stone Company That Matters

Kays of Scotland was founded in 1851 by William Kay and his sons Andrew and Thomas in Mauchline, East Ayrshire. They received permission from the Marquess of Ailsa to quarry granite from the island and began handcrafting curling stones.

For 175 years, Kays has been making curling stones. They're now the only company with rights to quarry Ailsa Craig granite, and they hold those rights through 2050.

Kays produces 2,000 to 2,500 stones per year for 77 countries. They've supplied stones to every Winter Olympics since Chamonix 1924 (except Salt Lake City 2002, for logistical reasons). For the 2026 Milano Cortina Olympics, Kays crafted all 132 stones used in competition.

The stones aren't cheap. A single Olympic-grade curling stone costs around $700-900. A full set of 16 stones for one sheet of ice runs about $12,000-14,000. But they last for decades if properly maintained.

The Three Granites of Ailsa Craig

Not all Ailsa Craig granite is the same. The island has three distinct types, though geologically they're very similar:

1. Common Green

The most abundant type. It's greenish-gray with distinctive black speckles where rare minerals cluster together. These minerals (including one called arfvedsonite, named after the Swedish chemist who discovered lithium) give Common Green granite a "springy" quality. When stones made of Common Green collide, they bounce off each other in predictable ways.

Common Green is used for the body of curling stones, including the "striking band" where stones collide with each other. It needs to withstand impacts without chipping or cracking, and Common Green excels at this.

2. Blue Hone

Rarer and higher quality than Common Green. It's grayish-blue with smaller, more uniform crystals. Blue Hone has extremely low water absorption, which prevents erosion from repeatedly freezing water. It's also incredibly smooth when polished.

Blue Hone is used for the "running band," the bottom surface that actually touches the ice. It needs to glide smoothly and maintain its polish despite constant friction. Blue Hone is perfect for this.

3. Red Hone

This is just Blue Hone that's been stained reddish-brown by iron minerals (rust). It has similar properties to Blue Hone. Unfortunately, all the Red Hone has been quarried away. It's gone. Only Common Green and Blue Hone remain.

How Olympic Curling Stones Are Made

Modern Olympic curling stones are composite: Common Green body with Blue Hone inserts (called "Ailserts") for the running surface. This combines the best properties of both granites.

The manufacturing process takes about six hours per stone:

Step 1: Quarrying

Harvesting granite from Ailsa Craig happens approximately once per decade. The most recent harvest was in 2020. Quarrying is strictly controlled because the island is a bird sanctuary. No blasting is allowed (it would disturb the birds), so workers must carefully extract granite using quieter methods. Quarrying only happens between September and November to avoid seabird breeding season.

Step 2: Shaping

Machines cut the granite into rough stone shapes. Each stone is carefully shaped to standard dimensions: 278mm wide (about 11 inches), 136mm tall (about 5.4 inches).

Step 3: Joining

A circular piece of Blue Hone granite (the Ailsert) is inserted into the bottom of the Common Green body. This creates the running band that touches the ice. Some high-end stones have double Ailserts (one on each side) so the stone can be flipped and used from either side.

Step 4: Handle Installation

A hole is drilled into the top of the stone and a handle is attached. Handles are typically made of plastic or synthetic materials and can be removed and replaced.

Step 5: Polishing

The stones are meticulously polished using pumice and diamond pads. The running surface must be extremely smooth to glide properly on ice, but it's not perfectly smooth. Ice technicians actually score tiny grooves into the running band. The pattern of these grooves affects how the stone interacts with the ice, influencing friction and curl.

Step 6: Quality Control

Each stone is weighed (must be between 38 and 44 pounds, with most Olympic stones at exactly 44 pounds) and tested. For the Olympics, Kays makes more stones than needed and selects the best ones. For 2026, they made 80 stones and chose the best 66 for competition.

What Makes Ailsa Craig Granite So Special?

Granite is one of the most common rocks on Earth. You can find it in Italy, the United States, India, China, and countless other places. So why is Ailsa Craig granite the only choice for Olympic curling?

1. Molecular Structure

Ailsa Craig granite has an unusually tight, fine-grained structure. When the magma cooled 60 million years ago, it cooled quickly enough to form very small, tightly packed crystals. This creates a dense, hard rock that's incredibly resilient.

This density makes the granite:

• Resistant to chipping and cracking: When stones collide at high speed, they don't shatter or chip.

• Resistant to water absorption: The rock's impermeability prevents water from seeping in, freezing, and causing cracks.

• Resistant to temperature changes: The stone maintains its integrity despite constant exposure to freezing temperatures.

2. Chemical Composition

The Ailsa Craig magma was unusually low in aluminum compared to most granites. This led to the presence of uncommon minerals like arfvedsonite and riebeckite. Scientists aren't entirely sure why, but these minerals contribute to the granite's toughness and its distinctive behavior when polished.

The lack of quartz is also important. Quartz is a brittle mineral found in many granites. Ailsa Craig granite has relatively little quartz, reducing the risk of brittle fractures.

3. Polishing Characteristics

Ailsa Craig granite takes a polish beautifully and maintains that polish despite constant friction with ice. The running surface of a curling stone needs to be extremely smooth and stay smooth through hundreds of games.

When scored with grooves by ice technicians, Ailsa Craig granite produces a specific surface roughness that creates ideal friction with ice. Other granites might technically work, but they produce different roughness patterns when scored the same way, changing how the stone behaves.

4. The Curl

Here's the mysterious part: curling stones don't actually slide straight. They curve (or "curl") to the left or right depending on the rotation you give them when releasing.

Scientists still don't fully understand exactly why curling stones curl, but it has to do with how the running band interacts with microscopic ice pebbles on the playing surface. The unique properties of Ailsa Craig granite, particularly Blue Hone, create consistent, predictable curling behavior.

"No other stone curls like an Ailsa Craig stone," as Erika Brown said. Other stones might slide fine, but when they collide or curve, they behave differently. For competitive curling, where millimeters matter, this consistency is essential.

5. Bounce Characteristics

When curling stones collide (which happens frequently), they need to bounce off each other in predictable ways. The "springy" nature of Common Green granite, caused by those black mineral clusters, creates the right bounce.

"It's not just about the ability to withstand chips and cracks," explained Dr. Bob Gooday, a geological analyst at National Museums Scotland. "It also has to do with how it moves on the ice and how the stones bounce when they hit each other. Professional curlers have used other kinds of stones, which slide perfectly well, but when they hit each other, they don't bounce quite the same."

6. Tradition and Standardization

Part of Ailsa Craig's monopoly is tradition. The Royal Caledonian Curling Club, Scotland's governing body for the sport, required Ailsa Craig granite for competition stones starting in 1838. When the sport became Olympic in 1924, those rules carried over.

Could other granites technically work? Maybe. A 1890 study found that curlers all over Scotland used various local granites successfully. But once Ailsa Craig became the standard, any deviation from it would be controversial.

Athletes train for years with Ailsa Craig stones. They know exactly how they feel, how they curl, how they bounce. Switching to different granite would change the sport fundamentally. Nobody wants that.

Is There Another Source?

Technically, yes. There's one other quarry in the world that supplies granite for curling stones: Trefor, in North Wales.

Trefor granite (both "blue Trefor" and "red Trefor") has similar properties to Ailsa Craig granite. It's hard, dense, takes a good polish, and can be used for curling stones.

Canada Curling Stone Co. uses Trefor granite for the bodies of their stones (though they still use recycled Ailsa Craig granite for the running bands). Kays has used Trefor granite in the past, but supply problems led them to switch entirely to Ailsa Craig. However, Olympic rules require Ailsa Craig granite. So for World Curling Federation competitions and the Olympics, Trefor granite doesn't cut it. It's Ailsa Craig or nothing.

The Future: Will the Granite Run Out?

This is a legitimate concern. Ailsa Craig is small. Quarrying is heavily restricted to protect birds. The granite is finite.

Current estimates suggest that at the current harvest rate (once per decade), there's enough granite to last many more decades, possibly into the next century. The 2020 harvest provided enough material for years of stone production.

But eventually, the supply will dwindle. What happens then?

Option 1: Relax Olympic rules to allow Trefor granite or other sources.

Option 2: Develop synthetic alternatives that mimic Ailsa Craig granite's properties.

Option 3: Recycle old Ailsa Craig stones. Many existing stones are decades old and could be refurbished rather than making new ones.

Option 4: Drastically reduce production and make Ailsa Craig stones even more exclusive and expensive.

For now, Kays of Scotland isn't worried. They have exclusive rights to Ailsa Craig granite through 2050 and enough material to meet demand for years to come. But the clock is ticking on the fairy rock.

The Bottom Line

Olympic curling stones are 44-pound pieces of granite from a single tiny island off the coast of Scotland called Ailsa Craig.

The island formed 60 million years ago from volcanic magma that cooled into an exceptionally dense, fine-grained microgranite with unique properties.

One company, Kays of Scotland (founded 1851), has exclusive rights to quarry the island and handcrafts all Olympic curling stones, producing 2,000-2,500 stones per year for 77 countries.

Three types of granite exist on the island: Common Green (used for stone bodies), Blue Hone (used for running surfaces), and Red Hone (depleted).

What makes Ailsa Craig granite special:

• Tight molecular structure (resistant to damage, water, and temperature)

• Unique chemical composition (low aluminum, rare minerals)

• Excellent polishing characteristics

• Consistent curling behavior

• Predictable bounce when stones collide

• 186 years of tradition and standardization

While Trefor granite from Wales can also be used for curling stones, Olympic rules require Ailsa Craig granite.

The supply is limited. Quarrying is restricted to protect seabirds. At current rates, there's enough for decades, but eventually alternatives will be needed.

The next time you watch curling, remember: those stones sliding across the ice came from a tiny, uninhabited island that happens to have the world's only supply of granite with exactly the right properties.

It's a sport born in Scotland, standardized in Scotland, and still dependent on Scottish geology formed 60 million years ago.

The fairy rock holds the secret to curling. And as long as the granite lasts, Ailsa Craig will remain the most important island in Olympic sport that nobody's ever heard of.

Sources

CNN. (2026). All Olympic curling stones are made with granite from Ailsa Craig, a small uninhabited island. Retrieved from https://www.cnn.com/2026/02/11/science/curling-stones-science-winter-olympics

Kays of Scotland. Curling Stones. Retrieved from https://www.kaysscotland.com/curling-stones

National Museums Scotland. (2025). The Roaring Game: Scotland's curling stone island. Retrieved from https://www.nms.ac.uk/discover-catalogue/the-roaring-game-scotlands-curling-stone-island

Olympics.com. (2025). The origins of the Olympic curling stone: Why Ailsa Craig Granite is unique. Retrieved from https://www.olympics.com/en/milano-cortina-2026/news/the-remarkable-properties-and-origins-of-the-olympic-curling-stone

Science Friday. (2022). Getting to the Core of Olympic Curling Stones. Retrieved from https://www.sciencefriday.com/articles/getting-to-the-core-of-olympic-curling-stones/

Scientific American. (2026). The quirky geology behind Olympic curling stones. Retrieved from https://www.scientificamerican.com/article/the-quirky-geology-behind-olympic-curling-stones/

Team GB. Ailsa Craig: Olympic curling stones and the Scottish island that makes them. Retrieved from https://www.teamgb.com/article/ailsa-craig-everything-you-need-to-know-about-where-olympic-curling-stones/5EFRzBr6xItMWCr2XRyaTS

Wikipedia. (2026). Kays of Scotland. Retrieved from https://en.wikipedia.org/wiki/Kays_of_Scotland

Yahoo Sports. (2026). Olympic curling stones are made from granite found solely on 1 island off coast of Scotland. Retrieved from https://sports.yahoo.com/olympics/article/olympic-curling-stones-are-made-from-granite-found-solely-on-1-island-off-coast-of-scotland-202945231.html