IT is almost as synonymous with Ireland as St Patrick himself.

But despite myths attributing its origins to Stonehenge or Robert the Bruce, researchers at Glasgow University have discovered that the Blarney Stone, famous for giving you the "gift of the gab" if you kiss it, is 100% Irish.

The stone, which is embedded in the battlements of Blarney Castle, near Cork, is steeped in rumour and myth with little published evidence of its true nature.

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Amongst the various legends are that it is a 'bluestone' like those at Stonehenge or that it was part of the true Stone of Destiny, given to Cormac MacCarthy by a grateful Robert the Bruce following victory at the Battle of Bannockburn in 1314. Other accounts suggest associations with Moses, King David, or with the death of St Columba, but with no clear source.

Geologists at Glasgow University's Hunterian Museum have reveal the true nature of the Blarney Stone after studying the microscope slide, containing a slice of the stone ground so thin that it is transparent to light. Analysis indicates the Blarney Stone is limestone, made of the mineral calcite, and containing recrystallised and slightly deformed fragments of fossil brachiopod shells and bryozoans, all of which suggests it is very local indeed.

Dr John Faithfull, curator at the Hunterian, said: "This strongly supports views that the stone is made of local carboniferous limestone, about 330 million years old, and indicates that it has nothing to do with the Stonehenge bluestones, or the sandstone of the current 'Stone of Destiny', now in Edinburgh Castle."

The Hunterian has around 40,000 geological microscope slides, and the older ones are mostly catalogued in hand-written ledgers. The Blarney Stone slide had escaped notice until now, but it was spotted in the catalogues during a digitisation programme being carried out by an intern.

The slide is part of the rock and mineral thin-section collection put together by Professor Matthew Forster Heddle, of St. Andrews, one of the giants of 19th Century geology and chemistry in the UK,some time between 1850 and 1880..