A "Viking piggybank" with silver coins minted in Dublin around a thousand years ago has been officially declared an authentic treasure trove by officials from the Isle of Man.

Among the hoard are pennies bearing the profile of King Sitric Silkbeard who was the Norse King of Dublin between around 989 and 1036AD and who "can be seen appearing to be giving a wave from a thousand years ago", said coin expert Dr Kristin Bornholdt-Collins.

The hoard was the fourth such discovery by former UK police officer turned metal detectorist Kath Giles who found the buried treasure consisting of 87 silver coins, 13 pieces of cut, silver arm-rings or “hack silver” and associated artefacts on a private field on the Isle of Man in April.

It was the third major discovery of ancient treasure on the island in the past six months.

Under Manx law, it was subject to a formal treasure inquest which was held last week and declared treasure by the Isle of Man Coroner of Inquests Jayne Hughes after being reported to Manx National Heritage as a find of archeological interest.

The hoard was put on display for the first time at the inquest on July 14 and will now go on display in the new Viking Gallery at the Manx Museum.

The coins were minted in England, Dublin, Germany and the Isle of Man and are mostly silver pennies. They are all around 2cm in diameter and weigh about a gram each, with most of them dating from around the AD 990s to the 1030s.

King Cnut, King Aethelred II of England and also a Holy Roman Emperor, Otto of Saxony can also be seen on the coins.

Allison Fox, archaeology curator at Manx National Heritage, said: “This is a wonderful find which helps further our understanding of the surprisingly complex Viking Age economy in the Isle of Man and around the Irish Sea area.

“The cut, or hack-silver pieces found with the coins were part of a flexible system of payment, where the value depended on the weight and purity of silver. It is expected that the coins and the hack-silver have over 90pc silver content,” she added.

Dr Bornholdt Collins said the hoard appears to have been stashed away over time, like a modern-day piggybank, with the intention of retrieving them later.

“The Northern Mixed hoard is the fourth Viking-Age coin hoard to be found in the Isle of Man in the last 50 years. It may have been added to over time, like a piggybank, accounting for some of the older coins, though for the most part it is a direct reflection of what was circulating in and around Man in the late 1020s to 1030.

"Like the similarly dated, but much larger, Glenfaba deposit, found in 2003, the new hoard might be compared to a wallet containing all kinds of credit cards, notes and coins, perhaps of different nationalities, such as when you prepare to travel overseas, and shows the variety of currencies available to an Irish Sea trader or inhabitant of Man in this period.

"The two hoards together provide a rare chance to study the contents side by side, right down to the detail of the dies used to strike the coins. Having this much closely dated comparative material from separate finds is highly unusual and essentially ‘doubles’ the value of each find."

She added that the hack-silver or bullion found in the hoard could be seen as a Viking-era equivalent of today's cryptocurrency ‘"because bullion was especially convenient for international trade since it was practical for any size transaction and was decentralized, a currency without borders or political affiliation".