Olympic Curling Stones Made from Special Granite.

The "Running Surface"

The bottom of a curling stone, known as the running surface, should be made of a granite that absorbs very little water. Any water absorbed into the running surface might freeze, expand, fracture mineral grains, and produce pits on the bottom of the stone.

These pits create roughness on the running surface and compromise the stone’s performance. Maintaining a smooth surface is critical for consistent glide and precision during play.

The "Striking Surface"

The body of a curling stone should be made from an extremely tough granite capable of absorbing impacts with minimal damage to its mineral grains. Damaged grains can produce pits on the striking surface and alter how impact energy is absorbed.

Once a pit develops on the striking surface, that spot becomes vulnerable to further breakage. To preserve performance, damage should be repaired before it spreads.

Two Curling Stone Granite Localities

Granites with the required properties for curling stones have only been found in a few locations worldwide. Today, most curling stones are produced from granite quarried in two primary locations:

1. Ailsa Craig, an island in the Firth of Clyde between Ireland and Scotland.

2. Trefor Granite Quarry, located on the coast of Wales.

Curling Stone Manufacturers

Kays of Scotland, based in Mauchline, Ayrshire, has been manufacturing curling stones from Ailsa Craig granite since 1851. They have supplied stones for the Winter Olympics since 1924 and have been the exclusive Olympic provider since 2006.

Kays uses Ailsa Craig Blue Hone granite for the running surface and Ailsa Craig Common Green granite for the body. Their quarrying rights are granted exclusively by the Marquess of Ailsa.

The Canada Curling Stone Company has produced stones from Trefor Granite since 1992 and supplied stones for the 2002 Winter Olympics. They hold an exclusive agreement with Trefor Granite for material used in curling stone production.