Early 1900s? Faceted purple glass/paste gem, silver choker

Hi there! This belonged to my mother's grandmother, which situates it in the early 1900s, and that's literally all we know about it. A jeweller wouldn't appraise it because it's a glass gem, but it's a beautiful antique and I'd love to know more about it. I can find no stamps anywhere on the metal.

A central cushion-cut purple "gem" about 3x2.5cm is flanked by two hexagonal "gems" 8mm wide. The four silver links on either side of the central gems are embossed. The remaining chain is alternate "link" and "chain" links.