The diamond chain section can be seen in the photo below.
Today the chain has been shortened considerably to allow the jewel to be worn as a necklace which sits close to the throat.
Photos of the jewel worn as a necklace can be seen in the first and third photos in the following link https://www.google.com/search?q=Cartier+Vestey+Melba&client=firefox-b-ab&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjou_j5xe7bAhUMerwKHeIdCncQ_AUICigB&biw=1536&bih=750
Some of the gemstones were significant gifts.
According to Margaret Young-Sanchez the central pearl in the jewel was a gift from a German banker, Herr von Mendelssohn, who, according to The Australian 24 March 2018, was a descendant of the composer. Originally the pearl was unset and was said to be valued at 2,500 pounds. The large diamond pendant to the jewel was, according to Melba, the very first gift she received and was given to her by subscribers of the Theatre de la Monnaie in Brussels.
What surprised me was that, according to The Australian, the jewel was not signed by Cartier nor did it have any French jeweller's mark; however, there was family history that the jewel was made by Cartier and investigations with Cartier revealed the date when Melba commissioned the jewel and that she supplied the gemstones.