Karl Rothmüller (1860-1930), Eternal Entwined Snakes Brooch, German, c. 1900. Gold, Peridot, Diamond, Pearl. W 2.90 cm (1.14 in); L 3.30 cm (1.30 in) © Tadema Gallery.

The naturalistic snakes biting a large emerald cut fine green peridot The power & vitality of a good Lalique jewel. 

Literature: cf. Meyers Lexikon Schmucksachen II, brooch version with oval stone Serpentina - Snake Jewellery from around the World, Fritz Falk, 2011, ISBN 978-3-89790-354-8 silver & gold pendant version, p.126 
Schmuck in Deutschland und Osterreich 1895-1914, Ulrike von Hase, 1977, p. 256 no 417 Art Nouveau Jewelry, Vivienne Becker, 1985, p.227 Imperishable Beauty, Art Nouveau Jewelry, Yvonne J. Markowitz & Elyse Zorn Karlin, Museum of Fine Arts, Boston, 2008, p. 78 & 149