It is the biggest, heaviest - and with a legal tender value of $1 million dollars - the most valuable gold bullion coin in the world.

But, crafted by the Perth Mint, the Guinness World Record holding piece tips the scales at one tonne of 99.99 per cent pure gold - making it worth more than $50 million.

Perth Mint's one-tonne coin.

And now the Australian piece is going on a European tour.

The coin measures 80 centimetres in diameter and is more than 12 centimetres deep.

Featuring a design created by Stuart Devlin, goldsmith and jeweller to the Queen, the coin depicts a red kangaroo surrounded by rays of sunlight.