The pendant, dating from Anglo-Saxon times, is the fourth such cross to be discovered and probably belonged to a high official.
It was found in 1965 by Ronald Wray, now 86, as he trudged home across the fields with a bale of hay on his back. He noticed the pendant, which is decorated with garnets, glittering in the early-morning sun. Heavy rain had washed away the earth and the two-inch cross lay exposed.
Mr Wray, who lives on Holdnerness peninsula, near Hull, took it to a jewellery expert, who was unable to identify it, so he took it home and put it in a kitchen drawer, where it remained for the next 30 years.
In 1997 Mr Wray's granddaughter took it to a "finds day" at Hull Museum, where it was immediately identified as an important Anglo-Saxon cross dating from the 7th century and one of only four with the garnet inlay known to exist.
After a treasure trove inquest, Mr Wray was declared the legal owner of the cross and it is to be auctioned on 21 October.
He said yesterday: "I used to scour the countryside with a metal detector and found some interesting pieces. What was amazing about the cross was that I found it without the detector while walking with a bale of hay on my back."Reuse content