This highly detailed penannular brooch is based on a find from Atlingbo in Gotland. The original was made of bronze and is now housed at the Historical Museum in Stockholm. This brooch is excellent for fastening neck slits on tunics and dresses made of linen or wool, likely the manner in which it was worn during its time.
See: Penannular Brooch from Atlingbo at the Historical Museum
There are some similar finds. For example:
Penannular Brooch from Gotland 1 at the Historical Museum and Penannular Brooch from Gotland 2 at the Historical Museum
Made of bronze.