LONDON A mysterious 18th century necklace made from around 500 diamonds, some of which are believed to have been taken from a piece that contributed to Marie Antoinette's demise, will go on sale in November, Sotheby's said on Sept. 23. The piece, from a private Asian collection, will go under the hammer in Geneva on Nov. 11, with online bidding opening on the auction house's website on Oct. 25. The necklace, which is composed of three rows of diamonds finished with a diamond tassel at each end,