A worn metal round at first dismissed as an old button has been revealed to be a silver coin minted by Magnus Barefoot, Norways last Viking king. It is unique on the archaeological record of Norway.The coin was discovered by metal detectorist Morten Eek in a field near Utstein monastery. He and his fellow metal detector club members examined it on site and when they saw that one side was made of copper and had a dark dot in the center, they thought it was an old metal button which are common metal detector finds. It was put in a box with other buttons for later review.A few months later, the contents of the box were reexamined by club members and this time the button was found to have a cross engraved on one side with the remnants of an inscription. It matched illustrations of medieval coins in reference works. The back, however, was covered up by a thin copper plate and the edges folded over it.Archaeologists at the Museum of Archaeology, University of Stavanger confirmed that it was indeed a coin but it had been modified by adding the copper plate. There are two small notches on the rim that may be wear and tear from where it was fitted with a chain or loop.The visible side of the coin consists of a cross drawn with double lines and with semicircles or bowls at the ends of the cross arms. The bowls contain small dots. In the angles of the cross there are lines towards the middle which give the impression that there is a single cross under the double one.Known as a criss-cross or cross-over-cross motif, it was used on the reverse of Norwegian coins for about 40 years at the end of the 11th and beginning of the 12th century. Since the other side was covered and removing the copper plate would be too invasive as the alteration is part of the coins history, researchers X-rayed the coin. Imaging revealed a griffin engraved on the obverse. That identified it as a coin issued by Magnus Barefoot, king of Norway from 1093 to 1103.Magnus Barefoot coins are very rare, with about 100 known, and very few of them were found in Norway. Of the 100 or so Magnus Barefoot coins, only four were known with the criss-cross on one side and a griffin on the other. The Utstein coin is the fifth one, and the first ever found in Norway. The die matches one of the ones found in Denmark.