This small stud, surrounded by gold and garnets, is a great example of early work with millefiori. Millefiori means 'One thousand flowers'.
Millefiori is an early glasswork technique, which was also found in the Sutton Hoo haul.
It is likely that the millefiori stud would have decorated a larger item.
You can see the intricately patterned gold foil that backs the garnets here! Millefiori stud