Hi welcome to forum.
Celtic Brooches & Pins
To me looks like a
Sterling Silver Celtic Traditional Tara pin Brooch ; try a Google Image search.
THE TARA BROOCH
http://www.solvar.ie/pages/story-of-irish-jewellery/The Irish tradition of metal working goes back over three thousand years to the Bronze Age. In those days, everyday items, such as swords and knives, were made of iron. However, bronze, silver and gold were used in the design of brooches, pins, rings, buckles, crosses and chalices.
The Tara Brooch is a classic example of Bronze Age craftsmanship. Discovered around 1850 in Bettystown, Co. Meath, it is exquisitely made in silver and gilt, decorated with interlacing patterns, spiral and trumpet devices, silver framed glass studs and gold filigree.
Oel