Marcasite and Black Stone Brooch

I bought this brooch at least 40 years ago.

It looks like it was made from something else (see the back)

Looks great with a collared shirt

Condition

Has some missing pieces of marcasite and a little scratching on the stone. 

Not sure if it's silver. 

It's not magnetic but hasn't been tested. 

MEASUREMENTS

Approximately 4" across, 2" tall

This item is sold from a vintage boutique in Providence, RI.