Charming pietra dura pin or brooch in an unusual setting. The piece is diamond-shaped, onyx inlaid with stones in umber, white, green and blue. The are no missing or damaged pieces, and the inlay is quite fine.
Pietra (sometimes petra) dura is an art of forming pictures with colored stones. The base is prepared and delicate pieces of stone are shaped and set. Pietra dura has been made since ancient times, and was often a treasured souvenir of Europe during the 1800's.
This little beauty is 1 5/8" x 1 1/8" (41mm x 30mm.The setting is low grade silver. It has been tested, and the results are unclear, but probably in the range of 70% silver. It is stamped "E.G.", but I find no information on this maker.
The locking ring clasp is newer and is a replacement, done in about 1920.