Vintg Pendant Necklace Blister Pearl Spiny Oyster Abalone Art Nouveau “STERLING”

Very Beautiful Pendant with Fantastic Colors, when it moves it reminds me of an Opal. The Sterling design surrounding it is amazing, looks Art Nouveau in design. I believe it’s a Spiny Oyster / Abalone Blister Pearl but I’m not a professional. I know it’s old and stunning. 19″ Chain marked “STERLING” on clasp. Pendant marked “STERLING” on back. Both are very worn markings. Thanks for looking!