A luck would have it I came across this auction sale in Switzerland.
[pdf-embedder url=“https://von-hoyer-boot.de/wp-content/uploads/2018/03/AMETHYST-GOLD-EMAIL-DIAMANT-BROSCHE-um-1900.-Gelbgold_.pdf“ title=“AMETHYST-GOLD-EMAIL-DIAMANT-BROSCHE, um 1900. Gelbgold_“]
Source: Koller Internationale Auktionen,
Zurich and Geneva,
Auction on 2. 12. 2008, 14:00