MARCASITE and STERLING Brooch with BLACK best Onyx and Marcasite Acorn Drop

I believe this could very well be English, I cannot quite make out the mark above the word Sterling. All done on sterling silver. Huge scalloped out like a wing and totally encrusted with marcasites. The dangle is a large egg shape with the top being all encrusted with marcasites and the bottom is best black onyx, this reminds me of an acorn. Measuring 3 1/4” by 3”. DROP DEAD GORGEOUS!