Beautiful Vintage Great Falls Metal Works Sterling Silver Onyx & Opal Brooch/Pin

Very nice modernist sterling silver brooch by Great Falls Metal Works. Center has onyx and opal. Marked on back "sterling" and "GFMW". Hard to see so I took a pic through my loop. The greens in the opal are beautiful. Took a few close-ups of that. I gently wiped with my silver polishing cloth. Will leave any additional cleaning up to the buyer. Please ask any questions.