Ailsa Craig (/ˈeɪlsə/; Scottish Gaelic: Creag Ealasaid) is an island of 99 hectares (240 acres) in the outer Firth of Clyde, 16 kilometres (10 miles) west of mainland Scotland, upon which blue hone granite was quarried to make curling stones. The now uninhabited island is formed from the volcanic plug of an extinct volcano.