C. 1840s. An exquisite French festoon necklace in its original antique box. The necklace is crafted with open-back green rock crystals surrounded by rose-cut diamonds in closed-back collet settings. The double-sided chain is 18k gold, with the stones set in silver tops backed by gold, a technique typical of this period. The diamonds possess a subtle, delicate sparkle, characteristic of their antique cut, and the soft green of the rock crystals is reflected in a captivating array of hues under various lights.
It is intriguing to see such an early and extensive usage of natural green rock crystal—not just one, but six stones—requiring a jeweler to have a rare collection of well-matched gems. This use of the stone is a special element that highlights the piece's rarity for this time period.
The necklace wears seamlessly, featuring a discreet clasp that does not interrupt the design. The push-in clasp is secure, closing with a satisfying click. The diamonds and natural rock crystals have all been lab-tested, confirming their authenticity.

The piece has been preserved in its original antique presentation box, complete with a lush green velvet interior. The box still bears the original label on the back: 'DUBIEF Joaillier Bijoutier, Rue Richelieu 84, a Paris'. Rue de Richelieu, particularly during the 19th century, was a street of great historical importance for the jewelry and luxury trades in Paris, often housing renowned artisans. The period associated with jewelers at 84, Rue de Richelieu was the height of the Romantic and Revivalist movements (roughly 1830s–1860s). 

The necklace measures approximately 15.85" at the top strand, and the approximate total weight of the rock crystals is 32 ct, with the largest center stone weighing about 6.5 ct. Overall, this piece remains in great condition, and lays beautifully around the neck.