Vintage 925 sterling silver Titan brooch/pin with black obsidian

Sterling silver brooch. Gold plated. Vintage, from the 50th or earlier. Stamped Titan STERLING on the back. With one natural black stone, which looks like obsidian. The pin closure is a bit tight (as it was stored for many years), but in fully working order. There is slight wear of the gold plating on the left side, but not very noticeable.