Vintage Art Deco crystal lavaliere or drop necklace from the 1920s or 1930s.  Faceted clear glass in geometric shapes, such as squares and rounds, set in an open-back style to maximize light reflection. 
The geometric shapes, clean lines, and dangling drop design are hallmarks of the Art Deco period, which prized symmetry and modern aesthetic.
Measures 39cm long and drop is 7cm. Extension can be arranged upon request.