It's estimated the necklace and matching earrings that are also being sold will fetch between $1.5 million and $2.5 million.
Diana didn't wear the earrings, because they weren't ready at the time.
The necklace has 164 diamonds, totaling 42.35 carats. Fourteen of the diamonds are marquise.
5 matching cultured pearls 12mm
11 marquise diamonds that total in 7.71 carat
3 marquise diamonds that total in 0.88 carat (these make up the clasp in the back)
The necklace is described as "a brilliant cut diamond and marquise diamond scroll motif center with a South Sea cultured pearl five stone and marquise diamond fringe drop, to a brilliant cut diamond two row collet back chain tapering to a single row; mounted in platinum, claw set, with an integral box clasp."
The necklace was made specifically for Diana by the royals' crown jeweler, David Thomas, and the director of a firm called Garrard. They wanted to capture Princess Diana's taste and incorporate South Sea pearls, which she loved.
On "The Early Show" Wednesday, co-anchor Erica Hill told her colleagues all about it - and even got to wear it!: