Vintage 12 karat gold filled necklace with vibrant ruby red crystals

Vintage necklace with vibrant red ruby color crystals. Not sure what they are made of. Filled with real 12 karat gold. 15" long. In very good condition, as pictured. Stamped 1/20 12K. Vintage gold filled jewelry is considered valuable and collectible as it tends to be of betyquality and contains quite a bit of real gold.