Yes, I think it's the diamond and emerald necklace. The elongated diamond links of the rear section are clearly distinguishable, as is the hook which connects the front with the rear section. Great find, and an interesting piece.

It was sold at Sotheby's »Magnificent Jewels« auction in Geneva on 17 November 2005 (Estimate 200.000–250.000 CHF, Lot sold 406.400 CHF).

Here's the link to Lot 447. Sotheby's cites a Van Cleef & Arpels exhibition catalogue and Sylvie Raulet's book about Van Cleef & Arpels, but the necklace is apparently unsigned.