I am not an expert in antique jewelry so please look closely at the photos and judge for yourself. This looks to be set in an early form of acrylic and my guess is late 30s. The primitive and irregular hinge assembly are indicative of an early handmade piece. The piece has no damage of any kind and appears to have been worn very little or not at all. The stone is a gorgeous sparkling green and among the largest I have ever seen. Clearly marked Czechoslovakia on the back but another marking below is not legible.
This is truly an authentic and extraordinary find for a collector.