Vintage THEDA Sterling Marcasite & Abalone Carved Cameo Miraculous Medal Pendant Necklace

Vintage marked STERLING THEDA miraculous medal pendant- the pendant is about 7/8ths of an inch tall without the bail and the attached pendant bail. There are no missing marcasites. The cameo is carved abalone and the back is very shiny so I would assume it is rhodium plated to resist tarnish. The chain is also marked sterling on the clasp and measures approximately 18 inches long.